Add prefetch_apex_record/replay service

This change introduces new `prefetch_apex_record` and
`prefetch_apex_replay` services to handle the prefetching of the `/apex`
directory specifically.

The new `prefetch_apex_record` service is configured to:
- Use a dedicated tracing instance (`--tracing-instance prefetch_apex`)
  to run concurrently with the main prefetcher without conflicts.
- Only record I/O from the `/apex` directory (`--include-mount-prefix
  /apex`) to avoid redundant work.
- Store the recorded data in a separate file (`prefetch_apex.pack`).

Currently, `prefetch_apex_record/replay` service only supports
non-updatable pre-installed /apex.

Bug: 410475961
Test: Manually verified that `prefetch_apex.pack` is created in
`/metadata/prefetch` with CL:34621324

Change-Id: Idac964b030c950a040e48650281fe8cfb7139fe2