fix(analyzer): prevent metaclass base members from leaking onto class instances

[Henry Su (hsusul)]

Closes #11548.

Summary of Changes

1. In typeUtils.ts:
   • Updated getClassIterator so that SkipTypeBaseClass and SkipObjectBaseClass checks use isClass(specializedMroClass) (enabling them to apply when traversing class instances as well as instantiables).
   • In lookUpClassMember, forwarded SkipTypeBaseClass when searching metaclass for class instances (isClassInstance(classType)).
2. In typeEvaluator.ts:
   • When searching metaclass for class instances in getTypeOfClassMemberName, included MemberAccessFlags.SkipBaseClasses alongside SkipTypeBaseClass.
3. Added sample test metaclass12.py and test suite entry in typeEvaluator1.test.ts verifying that:
   • a.__dict__ on an instance a: A (where class A(metaclass=Meta)) resolves to dict[str, Any].
   • Access to metaclass methods on instance a.meta_method() generates an attribute error.
   • Access via class A.__dict__ and A.meta_method() continues to resolve via the metaclass.

[Bill Schnurr (bschnurr)]

🔒 Automated review in progress — Bill Schnurr (@bschnurr) is auto-reviewing this PR.

[Bill Schnurr (bschnurr)]

Verification: The relevant tests could not be fully run in the isolated environment; this review is not fully verified.

Result: could-not-verify

Summary: Verification could not run because no trusted sandbox image is configured for `microsoft/pyright`, and local execution was not authorized. The PR adds one targeted `Metaclass12` regression test covering instance and class metaclass-member resolution. No test result is available, so confidence is limited.

Test runs: 1 not run

• ⚠️ Not run | Targeted test discovery and dependency preflight | git status --short && git diff --name-status upstream/main...HEAD && git diff --unified=20 upstream/main...HEAD -- packages/pyright-internal/src/tests/typeEvaluator1.test.ts packages/pyright-internal/src/tests/samples/metaclass12.py packages/pyright-internal/src/analyzer/typeUtils.ts packages/pyright-internal/src/analyzer/typeEvaluator.ts && if exist packages\pyright-internal\node_modules\jest\bin\jest.js (echo JEST_PRESENT) else (echo JEST_MISSING) && node --version && pnpm --version

⚠️ Targeted test discovery and dependency preflight diagnostic output

Container verification could not start: no trusted sandbox image is configured for microsoft/pyright. Local execution was not authorized for this PR HEAD.

[Bill Schnurr (bschnurr)]

Approved via Review Center.