fix: reject non-integer bucket counts

[tomatotomata]

Description

Add dedicated validation for bucket_sort's bucket_count argument. Non-integer values now raise a clear TypeError before arithmetic or bucket allocation, including on empty inputs; booleans are rejected explicitly despite inheriting from int in Python. The existing behavior for positive integer counts is unchanged.

Issue reference

Closes #14970

Validation

• python -m doctest sorts/bucket_sort.py
• python -m ruff check sorts/bucket_sort.py
• git diff --check
• Direct checks for float, bool, string, empty-input, and valid integer inputs.

I used coding assistance to prepare this focused fix and reviewed the rendered diff and test output manually. The patch is limited to sorts/bucket_sort.py.