refactor(runtime): delete the dead in-place ApplyDelta seam; config change = respawn only (#665)

Since #516 a DriverConfig change is stop + respawn, so DriverSpawnPlan.ToApplyDelta
was always empty and the in-place path had no producer. #663 and #664 were both
latent bugs in it. This deletes it:
- host: ApplyChildDelta, _pendingDelta, HandleApplyResult and HandleDeltaApplied
- plan: DriverSpawnPlan.ToApplyDelta
- actor: the ApplyDelta, ApplyResult and DeltaApplied messages, the Connected
  reinit handler and the mid-connect AdoptConfigDuringInit
- tests: the actor tests that drove the seam

IDriver.ReinitializeAsync and each driver's implementation and unit tests stay.
Comments and docs that cited AdoptConfigDuringInit as the reason a driver must
release prior state at init now cite the IDriver contract and overlapping
retries, which still apply.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs

@@ -406,7 +406,7 @@ internal sealed class ParsedDeploymentArtifact : IDisposable
         // v3: each spec's DriverConfig is the MERGED config the driver factory binds from —
         // DriverConfig (protocol/channel) + per-Device DeviceConfig (endpoint) + the driver's authored
         // raw tags (RawTags array, keyed by RawPath) — folded once here via DriverDeviceConfigMerger so
-        // both spawn (TryCreate) and redeploy (ApplyDelta) hand the driver the same shape.
+        // the factory (TryCreate) and the init (InitializeRequested) hand the driver the same shape.
         var rawTagsByDriver = BuildRawTagsByDriver(root);
         var deviceRowsByDriver = BuildDeviceRowsByDriver(root);