guest-diag: non-blocking trace tail + 100ms scan loop + raw counter-page dump

- the trace tail (subprocess + 256KB read) ran inside the scan loop and
  blocked it for seconds exactly when the client's GR window appeared;
  moved to a background thread whose queue the loop drains.
- scan interval 250ms -> 100ms.
- track_waits sampler also dumps 512 raw bytes at page+0xe00 each sample:
  the per-slot reads disagreed with the bulk dump within one sample
  because host writes land between the two, and the raw dump is the only
  trustworthy view of the slot layout.

0 files changed, 0 insertions, 0 deletions