[ty] Optimize materialized recursive protocol comparisons

[carljm]

Comparing explicit receiver types on overloaded recursive protocol methods can repeatedly expand materialized protocol specializations until ty overflows its stack. This extends the non-recursive-member shortcut to eligible materialized assignability comparisons, avoiding that expansion while preserving inference constraints.

For two specializations of the same protocol, the shortcut checks the non-recursive target requirements against the complete source interface. It skips recursive requirements only when those constraints mention every type variable in both specializations, including through aliases, and imply the nominal type-argument relation. Opposite top-to-bottom materializations and comparisons that cannot establish this proof retain the full structural path.

On main, the added benchmark overflows the stack. With this change it completes in about 10 ms in a profiling build.

Part of astral-sh/ty#4269.

Test plan

• Overloaded recursive protocol methods with tuple-specialized receivers and a gradual fallback terminate and preserve the callback's return type.
• Generic inference retains evidence supplied only by recursive members for both top and bottom materializations, including aliased parameters and variables on the source side of contravariant comparisons.
• Source members that contain the protocol remain available when the corresponding target requirement is non-recursive.
• Assignability and constraint inference reject top-to-bottom comparisons when a fixed Any in a recursive method becomes an incompatible return requirement.
• An added benchmark checks the expanding recursive-overload case.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 97.79%. The percentage of expected errors that received a diagnostic held steady at 94.33%. The number of fully passing files held steady at 112/136.

[astral-sh-bot]

Memory usage report

Memory usage unchanged ✅

[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)