Add comprehensive test suite for bitchat

- Created test utilities and helpers for common test operations
- Implemented Binary Protocol tests covering encoding/decoding, compression, and padding
- Added Noise Protocol tests for handshake, encryption, and session management
- Created Public Chat E2E tests for broadcasting, routing, TTL, and mesh topologies
- Implemented Private Chat E2E tests for direct messaging, delivery ACKs, and retry logic
- Added Integration tests for multi-peer scenarios, network resilience, and mixed traffic patterns
- Created mock implementations for BluetoothMeshService and NoiseSession

Test coverage includes:
- Protocol layer (binary encoding, message serialization)
- Security layer (Noise handshake, encryption/decryption)
- Application layer (public/private messaging, delivery tracking)
- Network scenarios (mesh topology, partitions, churn)
- Performance and stress testing

bitchatTests/TestUtilities/TestConstants.swift

@@ -0,0 +1,33 @@
+//
+// TestConstants.swift
+// bitchatTests
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+
+struct TestConstants {
+    static let defaultTimeout: TimeInterval = 5.0
+    static let shortTimeout: TimeInterval = 1.0
+    static let longTimeout: TimeInterval = 10.0
+    
+    static let testPeerID1 = "PEER1234"
+    static let testPeerID2 = "PEER5678"
+    static let testPeerID3 = "PEER9012"
+    static let testPeerID4 = "PEER3456"
+    
+    static let testNickname1 = "Alice"
+    static let testNickname2 = "Bob"
+    static let testNickname3 = "Charlie"
+    static let testNickname4 = "David"
+    
+    static let testMessage1 = "Hello, World!"
+    static let testMessage2 = "How are you?"
+    static let testMessage3 = "This is a test message"
+    static let testLongMessage = String(repeating: "This is a long message. ", count: 100)
+    
+    static let testRoomID = "test-room"
+    static let testSignature = Data(repeating: 0xAB, count: 64)
+}