Fix all compilation errors and warnings in test suite

- Fixed mock service property overrides to match base class properties
- Added missing CryptoKit imports where needed
- Fixed immutable property assignments by creating new instances
- Replaced XCTAssertThrows with XCTAssertThrowsError
- Fixed DeliveryAck serialization method names (serialize -> encode)
- Fixed unused variable warnings
- Ensured all BitchatPacket modifications create new instances
- Fixed BitchatMessage property mutations by creating new instances

All test targets now build successfully for both iOS and macOS platforms.

.gitignore

@@ -2,6 +2,9 @@
 #
 # gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
 
+## implementation plans
+plans/
+
 ## User settings
 xcuserdata/
 
@@ -58,4 +61,4 @@ __pycache__/
 
 ## Temporary files
 *.tmp
-*.temp
+*.temp