Fix spurious CLS report of 0 after bfcache restore

[suhailopensource]

Fixes #785.

Restores the zero-arg wrapper inside doubleRAF() so its callback is always invoked with no arguments:

-  requestAnimationFrame(() => requestAnimationFrame(cb));
+  requestAnimationFrame(() => requestAnimationFrame(() => cb()));

Per @Mimori256's suggestion in #785 I've taken the doubleRAF() hardening as the primary fix rather than reverting the onCLS() call site, since it re-establishes the invariant for every call site. src/onCLS.ts is unchanged.

Tests

Added e2e coverage for both reportAllChanges values, as @tunetheweb requested:

• does not report a spurious zero value after bfcache restore (reportAllChanges === false) — the regression test. Fails on main (through both retries), passes with the fix.
• reports the initial zero value after bfcache restore (reportAllChanges === true) — guards against over-correcting, so the zero-value report is still emitted when reportAllChanges is true. Passes with and without the fix.

Drive-by

Also adds a missing await beaconCountIs(1) to reports zero if no layout shifts occurred on first visibility hidden (reportAllChanges === false). That test reads the beacon file without waiting for the beacon to arrive, unlike its reportAllChanges === true sibling which has exactly that wait — an unrelated pre-existing race (those lines date to 2020/2022) that I hit locally. Happy to split it out if you'd prefer.

Verification

npm run test:e2e -- --browsers=chrome: 5/5 spec files, 153 passing, 4 skipped. Build, lint, format:check and unit tests all green. Reverting only the doubleRAF change leaves the new reportAllChanges === false test failing and everything else green.