feat: add --wait-for-agent flag to exec command

[rgarcia]

Summary

Adds a --wait-for-agent flag to the exec command that allows the CLI to wait for the guest agent to become ready before executing commands.

Motivation

When a VM is still booting, the guest agent may not be ready immediately. Previously, hypeman exec would fail immediately if the agent wasn't responding. This was especially problematic for:

• Newly started VMs
• VMs running systemd images (which have longer boot times)
• Scripts that run hypeman exec immediately after hypeman run

Changes

• Added --wait-for-agent flag with a default of 30 seconds
• The flag accepts seconds (e.g., --wait-for-agent=60 for 60 seconds)
• Use --wait-for-agent=0 to fail immediately (old behavior)
• Added wait_for_agent field to the exec request JSON

Usage

# Default: waits up to 30 seconds for agent
hypeman exec my-instance whoami

# Wait up to 60 seconds
hypeman exec --wait-for-agent=60 my-instance whoami

# Fail immediately if agent not ready
hypeman exec --wait-for-agent=0 my-instance whoami

Dependencies

This PR depends on the server-side support in:

• feat: add systemd mode for full VM experience hypeman#50

The wait_for_agent field is passed to the exec endpoint, which will retry connecting to the guest agent on AgentConnectionError until the timeout expires.

---

Note

Introduces a configurable wait period for the guest agent before executing commands.

• Adds --wait-for-agent CLI flag (default 30s; 0 to fail immediately) to exec command
• Extends exec request with wait_for_agent field and sets it in handleExec based on the flag
• No other behavior changes; existing flags and execution flow remain intact

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