log: emit progress lines for node and link loading on project open

A large topology takes ~50s to open (dominated by docker daemon node
creation). Without any start marker the user sees no feedback that work
is in progress. Add two INFO lines: 'Loading N nodes...' before the node
pool and 'Creating N links...' before the bulk link prepare/dispatch.

gns3server/controller/project.py

@@ -1710,6 +1710,7 @@ class Project:
 
             # Create nodes in parallel with limited concurrency
             # to avoid overwhelming the system with too many simultaneous operations
+            log.info("Loading %d nodes...", len(nodes_to_create))
             pool = Pool(concurrency=100)
             for compute, name, node_id, node_data in nodes_to_create:
                 pool.append(self.add_node, compute, name, node_id, dump=False, **node_data)
@@ -1732,6 +1733,7 @@ class Project:
             # request. This replaces one HTTP round-trip per link (~5000 for a
             # 2500-link topology) with one round-trip per compute.
             link_data_list = [d for d in topology.get("links", []) if "link_id" in d.keys()]
+            log.info("Creating %d links...", len(link_data_list))
             sem = asyncio.Semaphore(100)
 
             async def _prepare_one(data):