fix(variation): track longest same-size shot run

[ketpatil77]

Summary

• track the longest run of equal shot sizes instead of counting all equal adjacent pairs
• report the true run length in the violation text
• add regression coverage for split pairs, true runs of three, and unspecified gaps

Testing

• C:\Users\Jayesh\AppData\Local\Programs\Python\Python314\python.exe -m pytest tests/tools/test_variation_checker.py

Closes #268

[calesthio]

Approved. I verified the reported variation-checker issue is real on main: separated same-size pairs are incorrectly accumulated into a "3 consecutive same-size shots" violation, while an actual run of three same-size shots is not flagged. On this PR, separated pairs no longer trigger the consecutive-shot violation, true runs of three are flagged, and an unspecified shot breaks the run as intended.

Reviewed per docs/PR_REVIEW_GUIDE.md. Local checks passed: tests/tools/test_variation_checker.py, tests/contracts/test_phase0_contracts.py, py_compile for the changed files, and git diff --check. python -m pytest tests/eval -q found no pytest-discoverable tests. GitHub's Validate Python check was still pending at review time.

[ketpatil77]

Rebased on current main to clear the merge conflict. Functional logic is unchanged; this only refreshes the branch onto latest upstream so the approved fix can merge cleanly.

[ketpatil77]

Rebased on latest main, resolved the lib/variation_checker.py conflict against upstream changes, and force-pushed the refreshed branch. The same variation fix and tests are still in place.