Config push notify pattern: replace stateful pub/sub with signal+ fetch (#760)

Replace the config push mechanism that broadcast the full config
blob on a 'state' class pub/sub queue with a lightweight notify
signal containing only the version number and affected config
types. Processors fetch the full config via request/response from
the config service when notified.

This eliminates the need for the pub/sub 'state' queue class and
stateful pub/sub services entirely. The config push queue moves
from 'state' to 'flow' class — a simple transient signal rather
than a retained message.  This solves the RabbitMQ
late-subscriber problem where restarting processes never received
the current config because their fresh queue had no historical
messages.

Key changes:
- ConfigPush schema: config dict replaced with types list
- Subscribe-then-fetch startup with retry: processors subscribe
  to notify queue, fetch config via request/response, then
  process buffered notifies with version comparison to avoid race
  conditions
- register_config_handler() accepts optional types parameter so
  handlers only fire when their config types change
- Short-lived config request/response clients to avoid subscriber
  contention on non-persistent response topics
- Config service passes affected types through put/delete/flow
  operations
- Gateway ConfigReceiver rewritten with same notify pattern and
  retry loop

Tests updated

New tests:
- register_config_handler: without types, with types, multiple
  types, multiple handlers
- on_config_notify: old/same version skipped, irrelevant types
  skipped (version still updated), relevant type triggers fetch,
  handler without types always called, mixed handler filtering,
  empty types invokes all, fetch failure handled gracefully
- fetch_config: returns config+version, raises on error response,
  stops client even on exception
- fetch_and_apply_config: applies to all handlers on startup,
  retries on failure

trustgraph-flow/trustgraph/config/service/config.py

@@ -148,18 +148,7 @@ class Configuration:
 
     async def handle_delete(self, v):
 
-        # for k in v.keys:
-        #     if k.type not in self or k.key not in self[k.type]:
-        #         return ConfigResponse(
-        #             version = None,
-        #             values = None,
-        #             directory = None,
-        #             config = None,
-        #             error = Error(
-        #                 type = "key-error",
-        #                 message = f"Key error"
-        #             )
-        #         )
+        types = list(set(k.type for k in v.keys))
 
         for k in v.keys:
 
@@ -167,20 +156,22 @@ class Configuration:
 
         await self.inc_version()
 
-        await self.push()
+        await self.push(types=types)
 
         return ConfigResponse(
         )
 
     async def handle_put(self, v):
 
+        types = list(set(k.type for k in v.values))
+
         for k in v.values:
 
             await self.table_store.put_config(k.type, k.key, k.value)
 
         await self.inc_version()
 
-        await self.push()
+        await self.push(types=types)
 
         return ConfigResponse(
         )