Don't cache partial protocol checks that skip __call__

[PGrayCS]

Fixes #22151

is_protocol_implementation(..., skip=["__call__"]) (used by constraint inference for a callable's builtins.function fallback) skips a member check but still recorded a positive subtype-cache entry. A later full check against the same protocol (e.g. OneArg[Any]) could then wrongly succeed through the cache, so a callable matched both items of a union of callback protocols. That produced conflicting constraints and Never, depending on evaluation order (and worker assignment with --num-workers).

The fix is to not record cache entries when skip is used, since the result is only valid for the partial check.

Tests: added testCallbackProtocolUnionInferenceOrderIndependent. It fails without the fix and passes with it. Also ran pytest -n auto mypy/test/testcheck.py -k "rotocol or Callable or Union or Infer or Generic": 1975 passed, 9 skipped, 1 xfailed.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

scipy-stubs (https://github.com/scipy/scipy-stubs)
+ tests/misc/test_submodules_empty.pyi:3: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports