refactor: remove runOnIdleState

Run on idle state is a feature that we don't want to support at this time. It's best to keep the public interface as minimal as possible before the release. If it turns out users wish to use a functionality like these we can always re-add it later.

api/src/main/java/io/camunda/zeebe/process/test/api/InMemoryEngine.java

@@ -29,15 +29,6 @@ public interface InMemoryEngine {
    */
   void increaseTime(Duration timeToAdd);
 
-  /**
-   * Runs the given function once the engine has reached an idle state.
-   *
-   * <p>For more info on the idle state refer to {@link IdleStateMonitor}
-   *
-   * @param callback the function that should be executed once an idle state has been reached
-   */
-  void runOnIdleState(Runnable callback);
-
   /**
    * Waits for the engine to reach an idle state.
    *

engine/src/main/java/io/camunda/zeebe/process/test/engine/InMemoryEngineImpl.java

@@ -101,16 +101,11 @@ public void increaseTime(final Duration timeToAdd) {
     clock.addTime(timeToAdd);
   }
 
-  @Override
-  public void runOnIdleState(final Runnable callback) {
-    idleStateMonitor.addCallback(callback);
-  }
-
   @Override
   public void waitForIdleState() {
     final CompletableFuture<Void> idleState = new CompletableFuture<>();
 
-    runOnIdleState(() -> idleState.complete(null));
+    idleStateMonitor.addCallback(() -> idleState.complete(null));
 
     idleState.join();
   }

extension-testcontainer/src/main/java/io.camunda.zeebe.process.test.extension.testcontainer/ContainerizedEngine.java

@@ -122,11 +122,6 @@ public void increaseTime(final Duration timeToAdd) {
     closeChannel(channel);
   }
 
-  @Override
-  public void runOnIdleState(final Runnable callback) {
-    // TODO remove this from interface?
-  }
-
   @Override
   public void waitForIdleState() {
     final ManagedChannel channel = getChannel();