Rely on typeshed/stubs for slice typing

[ilevkivskyi]

Fixes #2410

slice has been generic in typeshed for more than a year now. Also all builtin collections have precise slice[SupportsIndex | None] types for __getitem__(). So, I don't think we need to be "policing" slice anymore, it should be really responsibility of the stub maintainers now.

After some searching, I see there are still many plain slice annotations in the wild, so this will be a trade-off of false positives to false negatives, but I think this is a right trade-off, since status quo causes issues for pandas dataframes and similar APIs.

I also considered some "intermediate" solutions, where we would still enforce SupportsIndex in some situations, but can't find anything that wouldn't be overly complicated.

[ilevkivskyi]

cc @Dr-Irv

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
+ sympy/stats/stochastic_process_types.py:1255: error: Unused "type: ignore" comment  [unused-ignore]

pandas (https://github.com/pandas-dev/pandas)
+ pandas/tests/indexes/string/test_indexing.py:152: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:153: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:154: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:155: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:156: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:157: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:159: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:160: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:161: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:162: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:163: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:164: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:165: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:166: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/indexes/string/test_indexing.py:167: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/copy_view/test_indexing.py:410: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/copy_view/test_indexing.py:478: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/copy_view/test_indexing.py:480: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/copy_view/test_indexing.py:482: error: Unused "type: ignore" comment  [unused-ignore]
+ pandas/tests/copy_view/test_indexing.py:485: error: Unused "type: ignore" comment  [unused-ignore]

xarray (https://github.com/pydata/xarray)
+ xarray/tests/test_dataarray.py:1327: error: Unused "type: ignore" comment  [unused-ignore]
+ xarray/tests/test_dataarray.py:1346: error: Unused "type: ignore" comment  [unused-ignore]

freqtrade (https://github.com/freqtrade/freqtrade)
- freqtrade/strategy/strategy_helper.py:107: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/strategy/strategy_helper.py:108: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:119: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:120: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:135: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:136: error: Invalid index type "tuple[slice[Timestamp, str | bytes | date | timedelta | datetime64[date | int | None] | <7 more items> | None, None], str]" for "_LocIndexerFrame[DataFrame]"; expected type "tuple[int | str | str_ | Timestamp | tuple[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any], ...] | Callable[[DataFrame], Never], int | str | str_ | tuple[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any], ...]]"  [index]
- freqtrade/data/btanalysis/trade_parallelism.py:136: error: Invalid index type "tuple[slice[Timestamp, str | bytes | date | timedelta | datetime64[date | int | None] | <7 more items> | None, None], str]" for "_LocIndexerFrame[DataFrame]"; expected type "tuple[tuple[IndexOpsMixin[Any, Any] | Series[builtins.bool] | ndarray[tuple[Any, ...], dtype[numpy.bool[builtins.bool]]] | list[builtins.bool] | str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any] | Sequence[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any]] | slice[Any, Any, Any], ...], Hashable]"  [index]
- freqtrade/data/btanalysis/trade_parallelism.py:136: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:151: error: Slice index must be an integer, SupportsIndex or None  [misc]
- freqtrade/data/btanalysis/trade_parallelism.py:152: error: Invalid index type "tuple[slice[Timestamp, str | bytes | date | timedelta | datetime64[date | int | None] | <7 more items> | None, None], str]" for "_LocIndexerFrame[DataFrame]"; expected type "tuple[int | str | str_ | Timestamp | tuple[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any], ...] | Callable[[DataFrame], Never], int | str | str_ | tuple[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any], ...]]"  [index]
- freqtrade/data/btanalysis/trade_parallelism.py:152: error: Invalid index type "tuple[slice[Timestamp, str | bytes | date | timedelta | datetime64[date | int | None] | <7 more items> | None, None], str]" for "_LocIndexerFrame[DataFrame]"; expected type "tuple[tuple[IndexOpsMixin[Any, Any] | Series[builtins.bool] | ndarray[tuple[Any, ...], dtype[numpy.bool[builtins.bool]]] | list[builtins.bool] | str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any] | Sequence[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any]] | slice[Any, Any, Any], ...], Hashable]"  [index]
- freqtrade/data/btanalysis/trade_parallelism.py:152: error: Slice index must be an integer, SupportsIndex or None  [misc]

[ilevkivskyi]

mypy_primer is as expected.