fix(vite): include no-result load hooks in module timings

[SaKaNa-Y]

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When investigating slow module processing in the Vite module graph, time spent in a load hook can disappear from the module summary. This happens when the hook returns undefined or null and a later plugin or Vite's file reader supplies the code. Plugin details retain the call, but the module summary only receives loads with code results.

Store these load timings separately from code and include them when the module receives its source. Tie pending timings to the enclosing transform request and discard uncommitted timings when that request ends. A later request replaces the prior snapshot, including an error result from a failed load. This also applies when Vite reads a file directly and when writes share a batch. Module invalidation clears the timing data.

Related fixes: #599 includes timings from transform hooks that return no code. #607 includes timings from successful resolveId calls that return the input ID. Each PR targets main and can be reviewed and merged independently.

Validation on this branch:

• Real Vite tests for empty load results fail with the old implementation and pass with this change, with both plugin-provided code and native file reads.
• Memory and disk tests cover request isolation, invalidation, source preservation, and batched writes. A controlled-clock retry keeps the successful request's 5 ms and source code while plugin details retain both the failed 80 ms call and the successful call.
• pnpm test --run: 52 files passed, 366 tests passed, 2 skipped.
• pnpm lint, pnpm typecheck, and pnpm build passed.

Timings follow the enclosing transform request. This change does not define separate timing snapshots for repeated nested this.load() calls within that request.

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commit: e13d837