[Gambit-Checkmate]

Change

index_of passes a start argument to the sequence's index method. Python's range.index takes only a value, so every range lookup previously raised TypeError. Slice the range at the requested start, use its native lookup, and translate a match back to its original index. Range slicing preserves constant space and the native arithmetic lookup for integer values.

Fixes #454.

Validation

• The baseline reproduces the TypeError. Eleven new cases pass with the patch, covering positive and negative starts, descending and empty ranges, missing values, numeric equality, and a range larger than sys.maxsize.
• Python 3.13.13 on Windows: 3,335 tests and doctests passed with 100% coverage. All 48 focused index cases passed on Windows 3.11, 3.12 and 3.14. Linux 3.10 passed 132,678 comparisons against list behavior.
• Ruff lint/format, mypy, chaining stub freshness, strict Sphinx, sdist/wheel builds and diff checks passed.

OpenAI Codex (GPT-6 based) assisted with investigation, implementation, testing and drafting.

[coveralls]

coverage: 100.0%. remained the same — Gambit-Checkmate:fix/index-of-range-start into dgilland:develop