fix: refresh package type inference per compilation

[OskarEichler]

Fix

Prevent automatic module-system inference from reusing stale package.json types across rebuilds.

The current cache is process-wide. Webpack correctly watches the discovered package.json, but after that file changes and starts a new compilation, the loader reads the old cached type instead of the updated file. Different compilation root boundaries can likewise share an inference that was valid only for the compilation that populated it.

Implementation

Keep the existing path cache per compilation in a WeakMap. Sibling modules in one compilation still avoid repeated filesystem traversal, while a new compilation re-evaluates its watched package metadata. Completed compilations and their maps can be garbage-collected.

Verification

• Added a regression that changes a temporary package from type: module to type: commonjs between compilation contexts. It fails on current main and passes with this change.
• Full suite including headless Chrome HMR conformance: 123 tests across 14 suites, 26 snapshots passed.
• ESLint, Prettier, TypeScript, and whitespace checks passed.
• React Doctor: 100/100.

Compatibility / breaking changes

No public API, dependency, runtime, or supported-platform changes. Explicit esModule options and extension-based inference remain unchanged.

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