Add error-path diagnostics for cloud-hypervisor startup

[sjmiller609]

Summary

• add failure-only diagnostics around cloud-hypervisor create/boot requests
• capture context cancellation state, deadline info, socket/process health, and a short vmm.log tail on failure
• keep the normal success path unchanged

Testing

• go test ./lib/hypervisor/cloudhypervisor

Notes

• broader package tests in this worktree are currently blocked by existing missing embedded binaries for vz-shim/guest-agent

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Note

Low Risk
Low risk: adds failure-only logging/diagnostics around Cloud Hypervisor StartVM HTTP calls without changing the success path or VM control flow.

Overview
Improves Cloud Hypervisor startup troubleshooting by emitting failure-only diagnostics when CreateVM or BootVM requests error or return non-204.

The new diagnostics log context cancellation/deadline details, socket existence/dialability, CH process liveness, and a truncated tail of logs/vmm.log, with response bodies/errors truncated to limit log volume.

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[firetiger-agent]

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