fix(library): rebuild SymbolLibraryManager when cache is empty

When a project is opened for the first time (e.g. right after
create_project) the sym-lib-table may not exist on disk yet.
SymbolLibraryManager.__init__ succeeds but leaves self.libraries={}.

The original guard in use_project() was:

    if self.library_manager.project_path == project_path:
        return

Because the path already matched the newly-created manager, the
early-return fired and the manager was never rebuilt once the
sym-lib-table appeared.  All subsequent list_symbols / search calls
returned nothing.

Fix: also require that at least one library was loaded before
treating the cache as valid.

Adds three unit tests that cover:
- rebuild triggered when project_path matches but libraries={}
- no spurious rebuild when libraries are already loaded
- rebuild on project_path change (existing behaviour)

python/commands/library_symbol.py

@@ -607,7 +607,11 @@ class SymbolLibraryCommands:
         """
         if project_path is None:
             return
-        if self.library_manager.project_path == project_path:
+        # Patch (SER2RJ45): keep cache when project_path matches AND libraries were
+        # actually loaded. Original early-return skipped rebuild even when the cache
+        # was empty (e.g. first call after create_project, before sym-lib-table existed).
+        if (self.library_manager.project_path == project_path
+                and len(self.library_manager.libraries) > 0):
             return
         logger.info(f"Rebuilding SymbolLibraryManager for project: {project_path}")
         self.library_manager = SymbolLibraryManager(project_path=project_path)