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

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs

@@ -396,7 +396,7 @@ public sealed class CalculationDriverTests
     }
 
     /// <summary>The skip ledger must be REBUILT on ReinitializeAsync, not just at construction — an
-    /// ApplyDelta that drops a tag's scriptId (or adds a new tag with none) must be reflected immediately,
+    /// in-place config change that drops a tag's scriptId (or adds a new tag with none) must be reflected immediately,
     /// since RebuildTagTable is the one routine both the ctor and reinit share.</summary>
     [Fact]
     public async Task GetSkippedTags_updates_after_reinitialize()
@@ -414,9 +414,9 @@ public sealed class CalculationDriverTests
     }
 
     /// <summary>
-    ///     Gitea #664 — <c>InitializeAsync</c> re-runs on a LIVE driver with a new config when an ApplyDelta lands
-    ///     mid-connect (<c>DriverInstanceActor.AdoptConfigDuringInit</c>). It used to ignore the JSON, so the
-    ///     driver kept its constructor tag set while the deploy reported the change applied. A config with a body
+    ///     Gitea #664 — <c>InitializeAsync</c> must serve the config document it is handed (the <c>IDriver</c>
+    ///     contract). It used to ignore the JSON, so a live driver re-initialised with a new config kept its
+    ///     constructor tag set. A config with a body
     ///     now rebuilds the tag table (and the dependency-ref set the host re-registers from).
     /// </summary>
     [Fact]