marker: batch topology dumps in bulk fan-out (per-def on 500+ links was ~1 minute)

Every per-link marker operation (start_marker / stop_marker / update_marker) called Project.dump() -- a full topology serialization + file write. A definition fan-out over 500 links therefore wrote the whole topology 500+ times (each blocking the event loop), which dominated the observed ~1 minute; the NIO round-trips themselves were negligible.

Add a dump: bool = True parameter to the three per-link operations and inherit_marker (matching the existing dump param on Link.add_node). The bulk paths -- definition create fan-out, definition-update sync and re-fan-out, definition-delete cleanup, pause/resume, new-link inheritance -- pass dump=False and their caller dumps once after. apply_defs_to_new_link suppresses per-def dumps too: link create / project open dump once after, so opening a 500-link project with N definitions no longer does 500xN topology writes.

gns3server/controller/link.py

@@ -114,7 +114,7 @@ class Link:
         """
         return self._markers
 
-    async def inherit_marker(self, def_name, marker_def):
+    async def inherit_marker(self, def_name, marker_def, dump=True):
         """
         Apply a project-level marker definition to this link.
 
@@ -147,6 +147,7 @@ class Link:
             highlight_duration=marker_def.get("highlight_duration"),
             enabled=not marker_def.get("paused", False),
             inherited_from=def_name,
+            dump=dump,
         )
 
     def _persist_markers(self):