tests: Add integration tests for port forwarding

Add comprehensive integration tests for the libvirt port forwarding feature:

1. test_libvirt_port_forward_parsing: Validates CLI argument parsing
   for various valid port forwarding formats (--port 8080:80, -p 80:80, etc.)

2. test_libvirt_port_forward_invalid: Tests error handling for invalid
   port formats (missing port, invalid numbers, out of range, etc.)

3. test_libvirt_port_forward_xml: Verifies that port forwarding is
   correctly configured in the libvirt domain XML with QEMU hostfwd args

4. test_libvirt_port_forward_connectivity: End-to-end test that creates
   a VM with port forwarding, starts an HTTP server inside the VM, and
   verifies connectivity from the host through the forwarded port

The tests follow the existing integration test patterns using the
distributed slice mechanism for test registration and include proper
cleanup of test VMs.

Assisted-by: Claude Code
Signed-off-by: ckyrouac <[email protected]>

Author: ckyrouac

crates/integration-tests/src/main.rs

@@ -17,6 +17,7 @@ use linkme::distributed_slice;
 
 mod tests {
     pub mod libvirt_base_disks;
+    pub mod libvirt_port_forward;
     pub mod libvirt_upload_disk;
     pub mod libvirt_verb;
     pub mod mount_feature;