Merge decision engine services into a single one

The decision engine process was built based on 2
services: a service that handle rpc requests and a
scheduler to trigger watcher periodic tasks.
With the new version of oslo.service, a new threading
backend was added, based on cotyledon service manager,
which starts a new process for each service tha it
manages. These two services can't run in different
process since they need access to a shared in-memory
representation of the cluster (cluster data models)
This patch proposes creating a Decision Engine Service
which includes everything in a single main service.

Change-Id: I335a97ca14b6e023fef055978a56aefebf22d433
Signed-off-by: Douglas Viroel <viroel@gmail.com>

watcher/decision_engine/service.py

@@ -0,0 +1,59 @@
+# Copyright 2025 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from watcher.common import service as watcher_service
+from watcher.decision_engine import manager
+from watcher.decision_engine import scheduling
+
+
+class DecisionEngineService(watcher_service.Service):
+    """Decision Engine Service that runs on a host.
+
+    The decision engine service holds a RPC server, a notification
+    listener server, a heartbeat service and starts a background scheduling
+    service to run watcher periodic jobs.
+    """
+
+    def __init__(self):
+        super().__init__(manager.DecisionEngineManager)
+        # Background scheduler starts the cluster model collector periodic
+        # task, an one shot task to cancel ongoing audits and a periodic
+        # check for expired action plans
+        self._bg_scheduler = None
+
+    @property
+    def bg_scheduler(self):
+        if self._bg_scheduler is None:
+            self._bg_scheduler = scheduling.DecisionEngineSchedulingService()
+        return self._bg_scheduler
+
+    def start(self):
+        """Start service."""
+        super().start()
+        self.bg_scheduler.start()
+
+    def stop(self):
+        """Stop service."""
+        super().stop()
+        self.bg_scheduler.stop()
+
+    def wait(self):
+        """Wait for service to complete."""
+        super().wait()
+        self.bg_scheduler.wait()
+
+    def reset(self):
+        """Reset service."""
+        super().reset()
+        self.bg_scheduler.reset()