test(debugger): pin the source-map wait debugger-status promises

[latekvo]

Found while reviewing #610 and set aside as out of scope: the code and the prose it comes from are byte-identical at that PR's merge base, and the same mutant survives there too.

The gap

debugger-status returns sourceMapReady: true as a hardcoded literal (debugger-status.ts:57). The only thing that makes the literal true is the line above it:

await api.sourceMaps.waitForPending();

and the description sells exactly that: "sourceMapReady (always true — waits for pending source maps before returning; no-op on Chromium)".

Nothing pins it. Deleting the await:

	existing suite (test/debugger test/metro test/flows test/utils)
unmutated	856 passed
await deleted	856 passed

So a status that reports readiness it never established would ship green.

Scope, stated honestly

This is a test-only change; the shipped behaviour is correct. The impact of a regression is narrow but real: js-runtime-debugger.ts:214 already drains the registry once while the service is being created, so the await in the tool is what covers maps registered after that point - a Fast Refresh, or a lazily loaded bundle chunk. In that window a non-awaiting status would return sourceMapReady: true while SourceMapsRegistry.pendingRegistrations is non-empty, and a debugger-inspect-element issued straight after can miss the file:line it would otherwise resolve.

I did not manufacture a user-visible failure end to end, and I am not claiming one - the finding is that the single promised behaviour of this field has no test.

The tests

Both assert the ordering, not the literal - a test that only checked sourceMapReady === true would pass on the mutant, since the literal is unconditional.

1. does not resolve until the pending source-map registration settles - hands the tool a waitForPending that returns a deferred promise, drains several macrotask turns, asserts the tool has not returned, then releases it.
2. reports sourceMapReady only after the wait - records ["maps-settled", "status-returned"] and asserts that exact order.

	new tests
on main as shipped	2 passed
with the await deleted	2 failed

eslint --max-warnings 0, tsc --noEmit -p tsconfig.test.json and prettier all clean.