[TESTS] Add JavaDocs for test objects

Add JavaDocs for the various Stub and Fake objects that are used
in the P2PDataStore test so future developers can understand why they
exist.

p2p/src/test/java/bisq/network/p2p/storage/mocks/AppendOnlyDataStoreServiceFake.java

@@ -24,6 +24,12 @@ import bisq.network.p2p.storage.persistence.AppendOnlyDataStoreService;
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * Implementation of an in-memory AppendOnlyDataStoreService that can be used in tests. Removes overhead
+ * involving files, resources, and services for tests that don't need it.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
+ */
 public class AppendOnlyDataStoreServiceFake extends AppendOnlyDataStoreService {
     private final Map<P2PDataStorage.ByteArray, PersistableNetworkPayload> map;
 

p2p/src/test/java/bisq/network/p2p/storage/mocks/ClockFake.java

@@ -21,6 +21,11 @@ import java.time.Clock;
 import java.time.Instant;
 import java.time.ZoneId;
 
+/**
+ * Fake implementation of the Clock object that can be used in tests that need finer control over the current time.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
+ */
 public class ClockFake extends Clock {
     private Instant currentInstant;
 

p2p/src/test/java/bisq/network/p2p/storage/mocks/DateTolerantPayloadStub.java

@@ -21,6 +21,13 @@ import bisq.network.p2p.storage.payload.DateTolerantPayload;
 
 import java.time.Clock;
 
+/**
+ * Stub implementation of a ProtectedStoragePayload implementing the DateTolerantPayload marker interface
+ * that can be used in tests to provide canned answers to calls. Useful if the tests don't care about the implementation
+ * details of the ProtectedStoragePayload.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
+ */
 public class DateTolerantPayloadStub implements DateTolerantPayload {
     private final boolean dateInTolerance;
 

p2p/src/test/java/bisq/network/p2p/storage/mocks/PersistableNetworkPayloadStub.java

@@ -19,6 +19,13 @@ package bisq.network.p2p.storage.mocks;
 
 import bisq.network.p2p.storage.payload.PersistableNetworkPayload;
 
+/**
+ * Stub implementation of a PersistableNetworkPayload that can be used in tests
+ * to provide canned answers to calls. Useful if the tests don't care about the implementation
+ *  * details of the PersistableNetworkPayload.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
+ */
 public class PersistableNetworkPayloadStub implements PersistableNetworkPayload {
     private final boolean hashSizeValid;
 

p2p/src/test/java/bisq/network/p2p/storage/mocks/ProtectedDataStoreServiceFake.java

@@ -24,6 +24,12 @@ import bisq.network.p2p.storage.persistence.ProtectedDataStoreService;
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * Implementation of an in-memory ProtectedDataStoreService that can be used in tests. Removes overhead
+ * involving files, resources, and services for tests that don't need it.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
+ */
 public class ProtectedDataStoreServiceFake extends ProtectedDataStoreService {
     private final Map<P2PDataStorage.ByteArray, ProtectedStorageEntry> map;
 

p2p/src/test/java/bisq/network/p2p/storage/mocks/ProtectedStoragePayloadStub.java

@@ -34,8 +34,12 @@ import javax.annotation.Nullable;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
-/*
- * Stub ProtectedStoragePayload whose hash is equal to the ownerPubKey
+/**
+ * Stub implementation of a ProtectedStoragePayload that can be used in tests
+ * to provide canned answers to calls. Useful if the tests don't care about the implementation
+ * details of the ProtectedStoragePayload.
+ *
+ * @see <a href="https://martinfowler.com/articles/mocksArentStubs.html#TheDifferenceBetweenMocksAndStubs">Reference</a>
  */
 public class ProtectedStoragePayloadStub implements ProtectedStoragePayload {
     @Getter