[ty] Synthesize read-only properties for all declared members on NamedTuple classes

[AlexWaygood]

Summary

Currently we treat declared attributes on NamedTuple classes just like declared attributes on any other class. But this is not correct! At runtime, the NamedTuple machinery synthesizes a read-only property for each attribute declared on a NamedTuple class. This PR implements that behaviour.

Test Plan

Mdtests

[github-actions]

Diagnostic diff on typing conformance tests

Changes were detected when running ty on typing conformance tests

--- old-output.txt	2025-08-14 21:23:47.772361962 +0000
+++ new-output.txt	2025-08-14 21:23:47.841362883 +0000
@@ -1,5 +1,5 @@
 WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
-fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/918d35d/src/function/execute.rs:215:25 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(71d5)): execute: too many cycle iterations`
+fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/918d35d/src/function/execute.rs:215:25 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(682a)): execute: too many cycle iterations`
 _directives_deprecated_library.py:15:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
 _directives_deprecated_library.py:30:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
 _directives_deprecated_library.py:36:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@__add__`
@@ -676,6 +676,7 @@
 namedtuples_type_compat.py:23:1: error[invalid-assignment] Object of type `Point` is not assignable to `tuple[int, str, str]`
 namedtuples_usage.py:34:7: error[index-out-of-bounds] Index 3 is out of bounds for tuple `Point` with length 3
 namedtuples_usage.py:35:7: error[index-out-of-bounds] Index -4 is out of bounds for tuple `Point` with length 3
+namedtuples_usage.py:40:1: error[invalid-assignment] Invalid assignment to data descriptor attribute `x` on type `Point` with custom `__set__` method
 namedtuples_usage.py:41:1: error[invalid-assignment] Cannot assign to object of type `Point` with no `__setitem__` method
 namedtuples_usage.py:52:1: error[invalid-assignment] Too many values to unpack: Expected 2
 namedtuples_usage.py:53:1: error[invalid-assignment] Not enough values to unpack: Expected 4
@@ -859,5 +860,5 @@
 typeddicts_operations.py:60:1: error[type-assertion-failure] Argument does not have asserted type `str | None`
 typeddicts_type_consistency.py:101:1: error[invalid-assignment] Object of type `Unknown | None` is not assignable to `str`
 typeddicts_usage.py:40:24: error[invalid-type-form] The special form `typing.TypedDict` is not allowed in type expressions. Did you mean to use a concrete TypedDict or `collections.abc.Mapping[str, object]` instead?
-Found 860 diagnostics
+Found 861 diagnostics
 WARN A fatal error occurred while checking some files. Not all project files were analyzed. See the diagnostics list above for details.

[github-actions]

mypy_primer results

No ecosystem changes detected ✅
No memory usage changes detected ✅

[AlexWaygood]

The new diagnostic in the typing conformance suite is correct -- this is a place where we previously had a false negative

[AlexWaygood]

There are some performance regressions of 1-2% on this PR due to the fact that we now need to eagerly check whether a class is an "exact NamedTuple" class (one that has NamedTuple directly in its class bases) on every attribute access on a class. #19901 (stacked on top of this PR) improves the situation there by adding caching to the mechanism we use for checking whether a class is a NamedTuple class.

[AlexWaygood]

Only 1% regressions on Codspeed after rebasing on top of #19912.

[carljm]

Very nice!