Group comparisons across intervening comments

[adenzhou1350]

Fixes #604.

Comments between a comparison operator and its operand prevented the comparison from being grouped. SELECT columns then became nested identifier lists, causing subsequent columns to drift right even with strip_comments=True.

Skip existing comment tokens while finding comparison operands, but retain them inside the group. Other grouping passes keep their existing behavior. Tests cover block/line comments, hints, nested comparisons, different operand types, statement boundaries, and SELECT indentation.

Validation on Windows / Python 3.14:

• Full suite: 521 passed, 2 xfailed, 1 xpassed; the existing xfail/xpass results are unchanged.
• The same focused tests against the original source: 14 failed, 166 passed, 2 xfailed; against this change: 180 passed, 2 xfailed.
• Ruff and git diff --check pass.

AI-assisted implementation, independently reproduced and checked locally. No multi-platform CI or performance claim.