Properly preserve state when interrupted during a deletion. Also use best...

Properly preserve state when interrupted during a deletion. Also use best Bazel practices for reinitializing maps by reassigning, since just clearing can retain memory. When enqueuing deleted nodes, don't use more threads than there are nodes. Finally, fix a test accidentally changed in https://github.com/bazelbuild/bazel/commit/3ea75594bfdb5e6794250155995c45a5adc00c28.

PiperOrigin-RevId: 392680387