0.87.16 followup. Extract the four debounce-race invariants
(predecessor abort, late-result suppression, AbortError swallow,
ownership-aware finally) from `loadCoverage` into a reusable
`CancellableLoader` helper at $lib/util/cancellable, with 9 unit
tests covering each. Page rewrite uses the helper.
Also corrects: hooks.server.test.ts (added Node-fetch rejection
shape for already-aborted entry; removed redundant tick); admin.test.ts
(AbortError-propagation now uses pre-aborted signal + mockRejectedValueOnce
mirroring real Node fetch).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>