refactor: use typing.Self on ModelDeploymentStatus.from_lifecycle

Address review comment — switch the explicit forward reference return
annotation to ``Self`` so subclasses get the proper return type without
the string literal. Route through the enum constructor (``cls(name)``)
with a small lookup table so mypy can keep the ``Self`` return type
without choking on the narrower ``Literal[ModelDeploymentStatus.X]``
inferred from direct ``cls.X`` returns.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: jopemachine

src/ai/backend/common/data/model_deployment/types.py

@@ -32,6 +32,20 @@ class ActivenessStatus(CIStrEnum):
     "created": "PENDING",  # never-deployed initial state
 }
 
+# Project ``EndpointLifecycle`` onto the v2 status name fed into the enum
+# constructor. ``SCALING`` lifecycle folds into ``READY`` because replica
+# reconciliation is exposed on the orthogonal ``scaling_state`` axis instead
+# of the lifecycle axis; ``CREATED`` (never-deployed) folds into ``PENDING``.
+_LIFECYCLE_TO_DEPLOYMENT_STATUS_NAME: dict[EndpointLifecycle, str] = {
+    EndpointLifecycle.PENDING: "PENDING",
+    EndpointLifecycle.CREATED: "PENDING",
+    EndpointLifecycle.READY: "READY",
+    EndpointLifecycle.SCALING: "READY",
+    EndpointLifecycle.DEPLOYING: "DEPLOYING",
+    EndpointLifecycle.DESTROYING: "STOPPING",
+    EndpointLifecycle.DESTROYED: "STOPPED",
+}
+
 
 class ModelDeploymentStatus(CIStrEnum):
     PENDING = "PENDING"
@@ -50,18 +64,8 @@ def _missing_(cls, value: Any) -> Self | None:
         return super()._missing_(value)
 
     @classmethod
-    def from_lifecycle(cls, lifecycle: EndpointLifecycle) -> "ModelDeploymentStatus":
-        match lifecycle:
-            case EndpointLifecycle.PENDING | EndpointLifecycle.CREATED:
-                return cls.PENDING
-            case EndpointLifecycle.READY | EndpointLifecycle.SCALING:
-                return cls.READY
-            case EndpointLifecycle.DEPLOYING:
-                return cls.DEPLOYING
-            case EndpointLifecycle.DESTROYING:
-                return cls.STOPPING
-            case EndpointLifecycle.DESTROYED:
-                return cls.STOPPED
+    def from_lifecycle(cls, lifecycle: EndpointLifecycle) -> Self:
+        return cls(_LIFECYCLE_TO_DEPLOYMENT_STATUS_NAME[lifecycle])
 
 
 class DeploymentStrategy(CIStrEnum):