tools: arm UVM kprobes deterministically (modprobe+wait+verify) and retry pushbuffer pins

Root cause of the cudaMalloc/UVM-init stall on our bring-up path:
guest_kprobes.sh ran while nvidia_uvm was not yet loaded (it loads lazily
with the first CUDA client), so every probe add failed silently (symbols
not in kallsyms) and the host never got the #sem -> pushbuffer-pin
pipeline. The CE push page (0x120021db8) then never translated and the
guest spun forever at DEVICE.

- guest_kprobes.sh: modprobe nvidia_uvm, wait (bounded 30 s) for the
  uvmt symbol, install, and print KP_ARMED/KP_FAIL for bring-up checks.
- semfix_watch.pin_pushbuffer: retry transient/partial gva2gpa misses
  in-call (bounded passes with a short sleep) instead of aborting on the
  first all-miss block; report unresolved page counts.

Validated: 2/2 cold boots (vmkeep6/7) arm the probes and run
victory_mail green in 15-20 s (MAIL + VADD bad=0 checksum=12204516 +
STATUS OK, oracle-matched); pre-fix boots with unarmed probes stalled
4/4.

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