[AAP-68258] Fix SonarCloud Reliability issues (#16354)

* Fix SonarCloud Reliability issues: time-dependent class attrs and dict comprehensions

- Move last_stats/last_flush from class body to __init__ in CallbackBrokerWorker
  (S8434: time-dependent expressions evaluated at class definition)
- Replace dict comprehensions with dict.fromkeys() in has_create.py
  (S7519: constant-value dict should use fromkeys)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix callback receiver tests to use flush(force=True)

Tests were implicitly relying on last_flush being a stale class-level
timestamp. Now that last_flush is set in __init__, the time-based flush
condition isn't met when flush() is called immediately after construction.
Use force=True to explicitly trigger an immediate flush in tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

awxkit/awxkit/api/mixins/has_create.py

@@ -61,7 +61,7 @@ def separate_async_optionals(creation_order):
             continue
         by_count = defaultdict(set)
         has_creates = [cand for cand in group if hasattr(cand, 'dependencies')]
-        counts = {has_create: 0 for has_create in has_creates}
+        counts = dict.fromkeys(has_creates, 0)
         for has_create in has_creates:
             for dependency in has_create.dependencies:
                 for compared in [cand for cand in has_creates if cand != has_create]:
@@ -212,7 +212,7 @@ class HasCreate(object):
         dependency_store = kw.get('ds')
         if dependency_store is None:
             deps = self.dependencies + self.optional_dependencies
-            self._dependency_store = {base_subclass: None for base_subclass in deps}
+            self._dependency_store = dict.fromkeys(deps)
             self.ds = DSAdapter(self.__class__.__name__, self._dependency_store)
         else:
             self._dependency_store = dependency_store.dependency_store