javadoc - Adding default constructor and javadoc for :plugin-api (#7072)

Signed-off-by: Usman Saleem <usman@usmans.info>

plugin-api/build.gradle

@@ -70,7 +70,7 @@ Calculated : ${currentHash}
 tasks.register('checkAPIChanges', FileStateChecker) {
   description = "Checks that the API for the Plugin-API project does not change without deliberate thought"
   files = sourceSets.main.allJava.files
-  knownHash = 'lRmKnDTcM8T+0wZqTBQYIK9SLnyxgUNQ9Cue93VMgwE='
+  knownHash = 'w+IKkNGNQSO4AECcQMEeYX0TriGTdBSFSx5e7e10yuk='
 }
 check.dependsOn('checkAPIChanges')
 

plugin-api/src/main/java/org/hyperledger/besu/plugin/data/BlockTraceResult.java

@@ -100,6 +100,9 @@ public class BlockTraceResult {
   public static class Builder {
     List<TransactionTraceResult> transactionTraceResults = new ArrayList<>();
 
+    /** Constructs a new builder instance. */
+    private Builder() {}
+
     /**
      * Adds a transaction trace result to the builder.
      *