Clamp M7 startup waits to absolute deadline

[jethac]

Summary

• clamp preflight request timeouts and retry sleeps to positive remaining readiness time
• propagate one absolute deadline through event, snapshot, inventory, and worker observations
• bound HTTP connect/read allocation and provider retry backoffs
• always issue one exact termination before deadline-bounded proof and retries

Verification

• 933 passed, 6 skipped
• Ruff passed
• compileall passed
• git diff --check passed

Deterministic fake-clock coverage includes zero/negative remaining time, slow calls, clock jumps, request timeouts, cancellation, and mandatory termination. No provider or BWS access.