Harden Fizz resource caches against prototype keys

[OskarEichler]

Summary

• Store request-local Fizz resource indexes in null-prototype dictionaries.
• Use React's shared safe ownership helper for every resource lookup.
• Cover DNS, connect, image, style, script, module, and unknown resource caches.
• Add a regression for hasOwnProperty and __proto__ URLs, including deduplication.

Breaking changes

None. Arbitrary resource strings that previously crashed or bypassed deduplication now behave as ordinary keys.

Verification

• Full ReactDOMFizzServer suite: 184 tests passed, including 2 snapshots.
• ReactDOMFloat suite: 142 tests passed, 1 skipped.
• Changed-source linc, Prettier, and git diff --check passed.

Fixes #37431

[github-actions]

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