fix(python): honor ValidJSON schemas across scorer call paths

[JianYan (JianYan11)]

Summary

Fix Python ValidJSON schema handling across constructor, keyword, positional, and partial scorer calls.

Two model-free repros on current main:

schema = {"type": "object", "required": ["answer"]}
ValidJSON(schema=schema).eval({}).score  # 1, but should be 0
ValidJSON().eval({}, schema=schema)     # TypeError: multiple values for 'schema'

The constructor saves self.schema but validation never reads it. Separately, Scorer.eval() forwards expected positionally, which collides with the schema parameter in ValidJSON._run_eval_sync(). The same collision affects async partial scorers.

Changes

• Match the base scorer's expected argument slot, preserving the existing second-positional-argument schema convention as a fallback.
• Use the constructor schema when no call-time schema is supplied.
• Keep explicit call-time schemas authoritative, including {}, True, and False; do not mutate the configured schema.
• Add sync, async, callable, partial, parsed-object and JSON-string regression coverage.

This is Python-specific argument plumbing. The TypeScript implementation already receives its schema in the scorer argument object and is unchanged. No scoring algorithm, dependency, or default validation policy changes.

Validation

• Initial regression run before the fix: 8 failed, 7 passed (constructor schema ignored and duplicate-argument failures).
• Final offline run: 26 passed, 1 deselected:

PYTHONPATH=py uv run --no-project --python 3.13 \
  --with polyleven --with chevron --with pyyaml --with jsonschema \
  --with pytest --with pytest-asyncio --with respx -- \
  python -m pytest py/autoevals/test_json.py py/autoevals/test_values.py \
  -k 'not test_list_contains' -q

• Changed files pass Black 24.10.0, Ruff, and git diff --check.
• test_list_contains was excluded after an initial run showed missing optional NumPy/SciPy dependencies. No live-model tests or full suite were run.

AI assistance: implemented and tested with OpenAI Codex.