Cleanup: declare __all__ for many scripts in tools/

tools/debug/gdb/blender_gdb_extension.py

@@ -21,6 +21,11 @@ To validate that things are registered correctly:
 3. Run `info frame-filter` and check for `blender-frame-filters`.
 '''
 
+__all__ = (
+    # Not used externally but functions as a `main`.
+    "register",
+)
+
 import gdb
 import functools
 from contextlib import contextmanager
@@ -675,4 +680,5 @@ def register():
     gdb.frame_filters[frame_filter.name] = frame_filter
 
 
-register()
+if __name__ == "__main__":
+    register()