test(project): Reproduce abort/retry delta over-write

[matz3]

Add a minimal reproduction of the build-server abort/retry over-write. A delta rebuild only re-processes the files that actually changed. When such a rebuild is aborted mid-flight and restarted, the retry re-processes ALL files the task handles instead of just the changed one. The served output stays correct (the retry writes the same bytes), so this is an optimization gap — redundant writes of unchanged files — rather than a correctness fault.

The replaceCopyright task substitutes ${copyright} in every file that contains it; the library.d fixture has two such files (some.js and .library). The test runs three builds:

1. Build once so the caches are warm.
2. A clean delta rebuild that changes only some.js. replaceCopyright writes only some.js. This already passes today.
3. The same delta, but aborted mid-build and retried. The retry should again write only some.js, but today it also re-writes .library.

Steps 2 and 3 use the same skipped-task set and expect the same written delta, so the aborted build differs from the clean one only in the replaceCopyright written set. That isolates the abort as the sole cause of the over-write. Both are asserted via the FixtureTester writtenResources assertion.

To drive the mid-build abort, requestResource gains an onBuildStatus hook that is attached for the duration of the request, so tests no longer hand-roll the process.on/off dance around byPath. _assertBuild dedupes the skipped-task list because an abort+retry emits one task-skip event per attempt.

Marked test.serial.failing until the abort/retry delta is optimized to re-process only the changed file.

JIRA: CPOUI5FOUNDATION-1363