feat: Add guest execution agent and vsock support

- Introduced a standalone guest execution agent to facilitate command execution within the guest VM over Firecracker's vsock.
- Enhanced FirecrackerClient to support vsock configuration, validating guest CID and UDS path.
- Updated configuration to include vsock settings by default.
- Refactored FirecrackerProcessManager to manage runtime sockets more effectively.
- Implemented guest agent installation and provisioning in the image store.
- Added API endpoints for executing commands in the VM and installing the guest agent.
- Improved error handling for guest execution failures and agent availability.

uvm/config.py

@@ -122,6 +122,9 @@ class Settings:
     def vm_dir(self, vm_id: str) -> Path:
         return self.vms_dir / vm_id
 
+    def guest_socket_path(self, vm_id: str) -> Path:
+        return self.vm_dir(vm_id) / "vsock.sock"
+
     @classmethod
     def from_environment(cls) -> "Settings":
         """Load optional deployment overrides while retaining script defaults."""