As the {CompilationTimeCallback} does not react to
{kFinishedCompilationChunk}, it does not need to stay alive after a
"final" compilation event.

Drive-by: Make the enum a boolean enum.

R=jkummerow@chromium.org

Bug: v8:12899
Change-Id: Iffacd6e3d9a0f2474a51f07cf01419b2badf98c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3667083
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80940}