Fix descriptor semantics for initialized annotations

[patrickswedish]

Summary

• avoid applying descriptor protocol semantics to annotated fields initialized in recognized instance methods
• preserve the existing class-field classification and class-level visibility behavior for unrelated annotations
• add regression coverage for annotation plus __init__ assignment while retaining annotation-only and method-only controls

Root cause

DeclaredByAnnotation already records initialized_in_recognized_method, but descriptor detection did not consult that signal. An annotation whose type implements __get__ was therefore treated as a class-installed descriptor even when self.field was initialized in __init__.

The fix uses that signal only to skip descriptor construction for the annotated-and-method-initialized case. It intentionally leaves the field's existing initialization classification unchanged, avoiding unrelated class-visibility and constructor behavior changes.

Fixes #4471

Validation

• cargo fmt --all -- --check — passed
• python test.py --no-test --no-tensor-shapes --no-conformance --no-jsonschema — formatting passed; Rust lint was blocked locally because the Windows host has no MSVC link.exe
• git diff --check — passed
• repository Linux, Windows, macOS, and compatibility CI rerunning on the narrowed patch

AI agent disclosure: OpenAI Codex prepared this PR; the contributor reviewed and understands the changes.

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Diff minimization and pre-flight validation performed with ZeroSlop™ CI — Ribbsaeter Systems.

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D115325693. (Because this pull request was imported automatically, there will not be any future comments.)

[codspeed]

Merging this PR will not alter performance

✅ 16 untouched benchmarks
⏩ 7 skipped benchmarks¹

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_{Comparing patrickswedish:codex/fix-annotated-descriptor-semantics (57c9c39) with main (0206f03)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[yangdanny97]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

This pull request has been merged in 8387bfd.

[patrickswedish]

Thanks for reviewing and merging, @yangdanny97! Glad to contribute.