Fix intcomma overflow for large Python integers

[Yananix]

Calling intcomma(10**400 + 123) with the default ndigits=None raises OverflowError because the non-finite check converts the integer to float. Python can format this integer directly with thousands separators, so the conversion imposes an unnecessary floating-point range limit.

Changes proposed in this pull request:

• Skip the float validation for values that are already Python integers. Integers are finite, and the existing integer formatting path preserves all digits.
• Add regression cases for positive and negative integers beyond the float range, checking the complete grouped output including the final 123.

Validation on Python 3.12:

• Both regression cases fail with OverflowError before the fix and pass after it.
• Compiled the translation catalogs with scripts/generate-translation-binaries.sh, then ran python -m pytest -q --benchmark-disable: 800 passed, no skips.
• Ruff, Black, and git diff --check passed for the changed files.

This patch is scoped to integer inputs with default precision. It does not change numeric-string parsing or explicit decimal-place formatting.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.57%. Comparing base (3201e70) to head (244ac0e).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #392   +/-   ##
=======================================
  Coverage   99.56%   99.57%           
=======================================
  Files          12       12           
  Lines         927      933    +6     
=======================================
+ Hits          923      929    +6     
  Misses          4        4           

Flag	Coverage Δ
macos-latest	97.64% <100.00%> (+0.01%)	⬆️
ubuntu-latest	97.64% <100.00%> (+0.01%)	⬆️
windows-latest	95.49% <100.00%> (+0.02%)	⬆️

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