Fix nullable NoInfer handler narrowing

[gvergnaud]

Summary

• Add a regression test for nullable NoInfer<User | null> | null values with P.nonNullable property patterns.
• Preserve useful handler narrowing when precise extraction falls back by intersecting safe inverted object patterns with the input type.
• Keep fallback behavior unchanged for never, any, unknown, primitive, and impossible object patterns.

Verification

• npm run check -- --noErrorTruncation
• npm test

Closes #354

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Summary by cubic

Fixes handler narrowing for nullable NoInfer objects when matching with P.nonNullable, so properties like name narrow to string as expected. Updates the MatchedValue fallback to preserve useful narrowing without changing behavior for never, any, unknown, primitives, or impossible patterns. Closes #354.

• Bug Fixes
  • Added a regression test for NoInfer<User | null> | null with { name: P.nonNullable }.
  • Adjusted MatchedValue to intersect a & invpattern only for safe object patterns.

^{Written for commit e0274cf. Summary will update on new commits.}