[ty] Fix identity narrowing for NewTypes

[charliermarsh]

Summary

NewType is nominal for static typing, but its constructor returns the input object unchanged at runtime. Prior to this change, we used ordinary type disjointness to evaluate and narrow is comparisons, so two distinct NewTypes with the same concrete base could be treated as unable to share an object and valid branches narrowed to Never:

from typing import NewType

class Foo: ...

FooNewType1 = NewType("FooNewType1", Foo)
FooNewType2 = NewType("FooNewType2", Foo)

foo = Foo()
foo1 = FooNewType1(foo)
foo2 = FooNewType2(foo)

reveal_type(foo1 is foo2)  # main: Literal[False]; this PR: bool
if foo1 is foo2:  # True at runtime
    reveal_type(foo1)  # main: Never; this PR: FooNewType1
    reveal_type(foo2)  # main: Never; this PR: FooNewType2

This PR projects NewTypes to their runtime representations before evaluating identity.

Closes astral-sh/ty#3552.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 94.47%. The percentage of expected errors that received a diagnostic held steady at 89.19%. The number of fully passing files held steady at 95/134.

[astral-sh-bot]

Memory usage report

Summary

Project	Old	New	Diff	Outcome
prefect	449.23MB	449.28MB	+0.01% (44.93kB)	⏫
sphinx	167.07MB	167.08MB	+0.01% (10.05kB)	⏫
trio	70.47MB	70.47MB	+0.01% (4.32kB)	⏫
flake8	29.02MB	29.03MB	+0.01% (1.77kB)	⏫

Significant changes

Click to expand detailed breakdown

prefect

Name	Old	New	Diff	Outcome
all_narrowing_constraints_for_expression	5.22MB	5.26MB	+0.77% (41.12kB)	⏫
infer_expression_types_impl	37.97MB	37.97MB	+0.00% (1.26kB)	⏫
infer_definition_types	49.99MB	49.99MB	+0.00% (784.00B)	⏫
UnionType	1.07MB	1.07MB	+0.07% (736.00B)	⏫
is_redundant_with_impl::interned_arguments	2.35MB	2.35MB	+0.01% (352.00B)	⏫
is_redundant_with_impl	1.31MB	1.31MB	+0.01% (192.00B)	⏫
IntersectionType<'db>::from_two_elements_::interned_arguments	13.32kB	13.49kB	+1.29% (176.00B)	⏫
loop_header_reachability	254.53kB	254.70kB	+0.06% (168.00B)	⏫
analyze_non_terminal_call	1.78MB	1.78MB	+0.01% (112.00B)	⏫
IntersectionType<'db>::from_two_elements_	9.74kB	9.84kB	+0.96% (96.00B)	⏫

sphinx

Name	Old	New	Diff	Outcome
all_narrowing_constraints_for_expression	1.94MB	1.95MB	+0.50% (9.92kB)	⏫
infer_expression_types_impl	14.89MB	14.89MB	-0.00% (576.00B)	⏫
IntersectionType	534.62kB	535.09kB	+0.09% (480.00B)	⏫
UnionType	583.61kB	583.95kB	+0.06% (352.00B)	⏫
is_redundant_with_impl::interned_arguments	1.14MB	1.14MB	+0.03% (352.00B)	⏫
infer_definition_types	13.69MB	13.69MB	-0.00% (336.00B)	⏫
is_redundant_with_impl	631.71kB	631.96kB	+0.04% (256.00B)	⏫
analyze_non_terminal_call	683.03kB	682.81kB	-0.03% (224.00B)	⏫
loop_header_reachability	228.74kB	228.58kB	-0.07% (168.00B)	⏫

trio

Name	Old	New	Diff	Outcome
all_narrowing_constraints_for_expression	462.36kB	466.50kB	+0.90% (4.14kB)	⏫
infer_expression_types_impl	4.42MB	4.42MB	+0.00% (112.00B)	⏫
infer_definition_types	3.97MB	3.97MB	+0.00% (48.00B)	⏫
loop_header_reachability	71.24kB	71.26kB	+0.03% (24.00B)	⏫

flake8

Name	Old	New	Diff	Outcome
all_narrowing_constraints_for_expression	74.68kB	76.45kB	+2.36% (1.77kB)	⏫

[astral-sh-bot]

ecosystem-analyzer results

No diagnostic changes detected ✅

Flaky changes detected. This PR summary excludes flaky changes; see the HTML report for details.

Full report with detailed diff (timing results)