feat: add errors parameter to CategoricalImputer for multimodal variables

[direkkakkar319-ops]

Description

Fixes #904

Adds an errors parameter to CategoricalImputer to handle multimodal categorical variables gracefully, instead of always raising a ValueError.

Changes

• Added errors parameter to CategoricalImputer.__init__() with options 'raise' (default), 'warn', and 'ignore'
• Updated both single-variable and multi-variable branches in .fit() to respect the new parameter
• When errors='warn', emits a UserWarning and imputes using the first most frequent category found
• When errors='ignore', silently imputes using the first most frequent category found
• Default errors='raise' preserves existing behaviour — no breaking changes
• Updated docstring with full parameter documentation
• Added tests covering all three errors values and invalid input
• Added CHANGELOG.rst entry

Type of Change

• Bug fix
• New feature (non-breaking)
• Breaking change
• Documentation update

Tests

All new and existing tests pass:

pytest tests/test_imputation/test_categorical_imputer.py

Notes

The existing error message ("contains multiple frequent categories") is preserved so no existing test matchers break.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.27%. Comparing base (f72a2b7) to head (a0ea71d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #908   +/-   ##
=======================================
  Coverage   98.27%   98.27%           
=======================================
  Files         116      116           
  Lines        4978     4988   +10     
  Branches      795      800    +5     
=======================================
+ Hits         4892     4902   +10     
  Misses         55       55           
  Partials       31       31           

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[direkkakkar319-ops]

@solegalli facing issue with the 2 checks will work on this and move the PR for review in some time

[direkkakkar319-ops]

the test pass percentage has increased still below the set benchmark
trying to resolve the problems