fix(model_splitter): copy on boundname remap

[wpbonelli]

Fix #2735

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.5%. Comparing base (556c088) to head (651cdb7).
⚠️ Report is 172 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2769      +/-   ##
===========================================
+ Coverage     55.5%    72.5%   +17.0%     
===========================================
  Files          644      677      +33     
  Lines       124135   132696    +8561     
===========================================
+ Hits         68947    96280   +27333     
+ Misses       55188    36416   -18772     

Files with missing lines	Coverage Δ
flopy/mf6/utils/model_splitter.py	65.4% <100.0%> (-9.5%)	⬇️

... and 579 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.