refactor: make RecordStream constructor private

This constructor is never accessed outside of this class. Other classes all use RecordStream.of().

filters/src/main/java/io/camunda/zeebe/process/test/filters/RecordStream.java

@@ -30,7 +30,7 @@ public class RecordStream {
 
   private RecordStreamSource recordStreamSource;
 
-  public RecordStream(final RecordStreamSource recordStreamSource) {
+  private RecordStream(final RecordStreamSource recordStreamSource) {
     this.recordStreamSource = recordStreamSource;
   }