refactor: address reviewer feedback on subscription.py

- Split subscribe_message_bindings into focused helper functions
- Add module-level constants for delivery modes and status codes
- Use WorkflowStatus enum instead of magic strings
- Add proper validation for dead_letter_topics (ValueError if multiple)
- Fix _resolve_event_loop to properly raise on missing loop
- Add zombie thread detection (raise RuntimeError on timeout)
- Move json import to top level
- Rename variables for clarity:
  - grouped -> bindings_by_topic_key
  - b -> binding
  - plan -> binding_schema_pairs
  - preferred -> matching_ce_type_pairs
- Replace logger.info with logger.debug for internal operations
- Restore underscore prefixes for internal functions
- Remove nested try/except where possible
- Add proper docstrings explaining function purposes

Signed-off-by: Arush Wadhawan <warush23+github@gmail.com>

Author: SoulSniper-V2

dapr_agents/workflow/utils/registration.py

@@ -25,7 +25,7 @@
     DedupeBackend,
     MessageRouteBinding,
     SchedulerFn,
-    resolve_loop,
+    _resolve_event_loop,
     subscribe_message_bindings,
 )
 
@@ -192,7 +192,7 @@ def _mount_http_bindings(
     if not bindings:
         return []
 
-    _ = resolve_loop(
+    _ = _resolve_event_loop(
         loop
     )  # Parity with message registrar; FastAPI does not require it yet.
     closers: List[Callable[[], None]] = []