chore: Remove dead install_types mypy config

[jsonbailey]

Summary

• Removes install_types = true and non_interactive = true from the [tool.mypy] section in all three package pyproject.toml files (server-ai, server-ai-openai, server-ai-langchain).
• These settings were inherited from the Poetry era. Poetry venvs include pip, so mypy's install_types mechanism could auto-install missing type stubs via python -m pip install. After the migration to uv (PR chore: Migrate from Poetry to uv workspace (PR-1) #101), uv-managed venvs do not include pip, making these settings a silent no-op.
• The AI SDK packages don't import any untyped third-party packages — launchdarkly-server-sdk, chevron, langchain, and openai all ship their own type information — so no explicit stubs need to be added; the settings can simply be removed.

Test plan

• make lint passes in packages/sdk/server-ai with no mypy errors