refactor: Pythonic cleanup of gematria.py and utils.py (regression-tested)

[Wolfvin]

Pythonic Cleanup — Verified Safe by Regression Testing

This PR contains behavior-preserving refactoring of gematria.py and utils.py, verified using Regrets — an output-fingerprint regression testing tool.

Changes to gematria.py

• Added module-level docstring with clear purpose description
• Extracted _SPECIAL_REPLACEMENTS dict for the divine-name-avoidance rule (15→טו, 16→טז), replacing hidden .replace() calls chained together
• Extracted _apply_special_replacements() as a dedicated, self-documenting function
• Named constants: _GERESH, _GERSHAYIM, _TAV — replacing inline Unicode characters that are hard to distinguish
• Improved variable names in _get_letters(): ones→ones_digit, tens→tens_digit, hundreds→hundreds_raw, four_hundreds→tav_count/tav_prefix
• Added comprehensive docstrings with parameter documentation
• Simplified _stringify_gematria() with early return for empty input

Changes to utils.py

• Simplified _is_leap() from redundant if (condition): return True; return False to direct return condition, with docstring explaining the 19-year Metonic cycle
• Extracted _apply_postponement() from _elapsed_days() — the three dehiyyah (postponement) rules (Molad Zakein, Gatarad, Betutakafot) are now in a separate, well-documented function with named boolean variables instead of a deeply nested conditional
• Used frozenset for month membership testing in _month_length() (O(1) lookup instead of O(n) list scan)
• Replaced nested if/return with Pythonic ternary expressions for variable-length months
• Simplified _month_name() with ternary name list selection
• Added comprehensive docstrings to all modified functions

3-Way Regression Test Verification

Using Regrets, I fingerprinted 7 behavioral clusters before refactoring, then verified after refactoring:

Cluster	Entry Function	Fingerprint	Status
gematria-convert	_num_to_str	69vpdvu	PASS
hebrew-leap	_is_leap	5wtkimf	PASS
month-length	_month_length	fny25om	PASS
month-name	_month_name	3pfo2au	PASS
elapsed-days	_elapsed_days	5hj9vhu	PASS
get-letters	_get_letters	2lcwua6	PASS
stringify-gematria	_stringify_gematria	5etsuwj	PASS

3 verifications all passed:

1. Regrets clusters: All 7 GREEN after refactoring
2. Raw output: Identical to pre-refactor baseline (KEBENARAN 1)
3. Fingerprint cross-check: All hashes match KEBENARAN 2 exactly

No behavioral changes — only code clarity and maintainability improvements.