Fix property access for function types

[daleselaji-dev]

Problem

Mypy treats a property returning types.FunctionType as a bound method when the value is accessed from an instance. A valid isinstance(..., FunctionType) assertion is therefore reported as an impossible intersection with MethodType when --warn-unreachable is enabled.

Root Cause

Member analysis can apply descriptor access a second time after a property getter has already produced its value. The original fix skipped that duplicate pass for read-only properties, but the first review repair also exposed an existing dataclass-transform descriptor case whose synthetic read-only field still needs descriptor access.

Solution

Skip the duplicate descriptor pass for ordinary read-only property results while preserving descriptor evaluation for fields recorded in the dataclass-transform metadata. This keeps the reported FunctionType property narrowing correct without regressing generic descriptor-backed dataclass fields.

Changes

• Avoid the second descriptor binding for ordinary read-only property results in analyze_var.
• Preserve descriptor access for synthetic dataclass fields by checking the field metadata.
• Keep the original focused FunctionType/MethodType regression and descriptor fixture.
• Fix the related CI regression on check-dataclass-transform.test.

Testing

• Reproduction before fix: current main revealed wrapped.__func__ as types.MethodType and emitted two [unreachable] errors.
• Property regression plus dataclass regression: pytest -n0 mypy/test/testcheck.py -k 'testPropertyReturningFunctionType or testDataclassTransformGenericDescriptor' — 3 passed.
• Full check-classes.test: 610 passed, 1 existing xfailed.
• Self typecheck: python -m mypy --config-file mypy_self_check.ini -p mypy — 196 source files, no issues.
• Ruff: not verified; the local environment has no Ruff module.
• git diff --check: passed.
• CI repair evidence: run 32691141642 failed consistently on the pre-existing check-dataclass-transform.test expectation after the original diff; the new same-scope head is 3f4c859 and the local regression is green.

Compatibility/Risk

Only static member-type analysis is changed. Ordinary read-only properties retain value semantics, settable properties retain their descriptor behavior, and synthetic dataclass-transform descriptor fields retain instance access through __get__. Runtime Python behavior is unchanged.

Notes for Reviewer

The added metadata check is intentionally narrow: it identifies a dataclass field by the existing info.metadata["dataclass"]["attributes"] record instead of broadening descriptor handling for every property. This contribution was AI-assisted.

Linked Issue

Fixes #21879

[github-actions]

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

colour (https://github.com/colour-science/colour)
- colour/continuous/signal.py:1207: error: Argument 1 to "as_float_array" has incompatible type "ndarray[tuple[int], dtype[Any]] | ExtensionArray"; expected "Buffer | _SupportsArray[dtype[Any]] | _NestedSequence[_SupportsArray[dtype[Any]]] | complex | bytes | str | _NestedSequence[complex | bytes | str]"  [arg-type]
+ colour/continuous/signal.py:1207: error: Argument 1 to "as_float_array" has incompatible type "ndarray[tuple[int], dtype[Any]] | ExtensionArray | Categorical[object]"; expected "Buffer | _SupportsArray[dtype[Any]] | _NestedSequence[_SupportsArray[dtype[Any]]] | complex | bytes | str | _NestedSequence[complex | bytes | str]"  [arg-type]

freqtrade (https://github.com/freqtrade/freqtrade)
+ freqtrade/freqai/freqai_interface.py:950: error: Argument 1 to "to_datetime" has incompatible type "Any | object"; expected "float | str | datetime | datetime64[Any] | date"  [arg-type]