Performance: accelerate project opening with parallel link creation and batch UDP port allocation

- Narrow IOU lock scope to only cover application_id allocation,
  allowing concurrent IOU node creation via Pool(concurrency=5)
- Parallelize link creation during project.open() using Pool(concurrency=5)
  instead of sequential processing
- Add batch UDP port allocation endpoint on compute to allocate N ports
  in a single HTTP call
- Pre-allocate UDP ports per compute before link creation during project
  loading, reducing HTTP round-trips
- UDPLink.create() falls back to individual port allocation if no
  pre-allocated port is available

gns3server/api/routes/compute/compute.py

@@ -55,6 +55,23 @@ def allocate_udp_port(project_id: UUID) -> dict:
     return {"udp_port": udp_port}
 
 
+@router.post("/projects/{project_id}/ports/udp/batch", status_code=status.HTTP_201_CREATED)
+def batch_allocate_udp_ports(project_id: UUID, body: dict) -> dict:
+    """
+    Allocate multiple UDP ports on the compute in a single call.
+
+    Used during project loading to pre-allocate all required UDP ports
+    before creating links, reducing HTTP round-trips.
+    """
+
+    count = body.get("count", 1)
+    pm = ProjectManager.instance()
+    project = pm.get_project(str(project_id))
+    m = PortManager.instance()
+    udp_ports = [m.get_free_udp_port(project) for _ in range(count)]
+    return {"udp_ports": udp_ports}
+
+
 @router.get("/network/interfaces")
 def network_interfaces() -> List[dict]:
     """