merge: #614

614: fix: implement InMemoryLogStorage.append r=korthout a=korthout

## Description

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This method was newly added to LogStorage to support appends of unserialized application data. But now this lead to a compilation error in ZPT because it contains a class `InMemoryLogStorage` that implements `LogStorage`.

The [implementation of the test class ListLogStorage](https://github.com/camunda/zeebe/blob/4dd1025f3f3ba86b5aec10d380b9db8550ed0967/logstreams/src/test/java/io/camunda/zeebe/logstreams/util/ListLogStorage.java#L77-L79) seemed like a reasonable solution for zeebe-process-test. It simply writes the contents of the writer into a buffer and appends it as usual.

## Related issues

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closes #613

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## Definition of Done

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Code changes:
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Testing:
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Co-authored-by: Nico Korthout <nico.korthout@camunda.com>

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

@@ -9,6 +9,7 @@
 
 import io.camunda.zeebe.logstreams.storage.LogStorage;
 import io.camunda.zeebe.logstreams.storage.LogStorageReader;
+import io.camunda.zeebe.util.buffer.BufferWriter;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -33,6 +34,17 @@ public LogStorageReader newReader() {
     return new ListLogStorageReader();
   }
 
+  @Override
+  public void append(
+      final long lowestPosition,
+      final long highestPosition,
+      final BufferWriter bufferWriter,
+      final AppendListener listener) {
+    final var buffer = ByteBuffer.allocate(bufferWriter.getLength());
+    bufferWriter.write(new UnsafeBuffer(buffer), 0);
+    append(lowestPosition, highestPosition, buffer, listener);
+  }
+
   @Override
   public void append(
       final long lowestPosition,