Complete the FakeRedis test double for the subsystem metrics pipe (#16745)

TestCallbackBrokerWorker::test_duplicate_key_not_saved_twice can crash
with AttributeError: 'FakeRedis' object has no attribute 'hincrby'.

CallbackBrokerWorker.flush() ends with

    if self.subsystem_metrics.should_pipe_execute() is True:
        self.subsystem_metrics.pipe_execute()

and should_pipe_execute() is True once more than
SUBSYSTEM_METRICS_INTERVAL_SAVE_TO_REDIS seconds have passed since the
last pipe execute. On a fast machine that interval never elapses during
the test, so the pipe is never executed and nothing notices; on a slow
one it does, pipe_execute() calls store_value() on every metric, and
IntM/FloatM/SetIntM reach for hincrby/hincrbyfloat/hset, which the
FakeRedis double in awx/main/tests/functional/conftest.py does not have.

Rather than suppress the pipe execute in the one test, make the double
complete enough to execute it: add the hash commands the metric
store_value() implementations use, an execute() for the pipeline
(pipeline() returns self), and a lock() returning a lock that never
acquires, so send_metrics() takes its "another thread holds the lock"
early return instead of trying to emit a websocket notification through
a channel layer that is not available under test.

awx/main/tests/functional/conftest.py

@@ -76,6 +76,16 @@ def swagger_autogen(requests=__SWAGGER_REQUESTS__):
     return requests
 
 
+class FakeLock:
+    # Never acquirable, so callers that guard work with a redis lock take the
+    # "someone else holds it" branch instead of reaching for real services.
+    def acquire(self, *args, **kwargs):
+        return False
+
+    def release(self, *args, **kwargs):
+        pass
+
+
 class FakeRedis:
     def __init__(self, *args, **kwargs):
         # Accept and ignore all arguments to match redis.Redis signature
@@ -90,6 +100,21 @@ class FakeRedis:
     def get(self, *args, **kwargs):
         return None
 
+    def hset(self, *args, **kwargs):
+        return 1
+
+    def hget(self, *args, **kwargs):
+        return None
+
+    def hincrby(self, *args, **kwargs):
+        return 0
+
+    def hincrbyfloat(self, *args, **kwargs):
+        return 0.0
+
+    def lock(self, *args, **kwargs):
+        return FakeLock()
+
     def rpush(self, *args, **kwargs):
         return 1
 
@@ -112,6 +137,9 @@ class FakeRedis:
     def pipeline(self):
         return self
 
+    def execute(self, *args, **kwargs):
+        return []
+
     def ping(self):
         return