Move exceptions to their own folder

[tudddorrr]

Exception infrastructure reorganisation

• Five exception classes (ContinuityReplayException, IdentifyException, PlayerAuthException, RequestException, SocketException) moved from Runtime/Utils/ into a dedicated Runtime/Exceptions/ directory, establishing a single, discoverable home for all custom exception types

Safer error-code parsing on PlayerAuthException and SocketException

• ErrorCode changed from a lazily-computed method (which parsed Message on every access) to a property set eagerly in the constructor, ensuring the code is captured once and is available even if the exception is rethrown or its message altered
• Enum.Parse replaced with Enum.TryParse so that unrecognised or malformed error-code strings gracefully fall back to API_ERROR instead of throwing a System.ArgumentException at the caller

Minor hardening on ContinuityReplayException

• The internal _exceptions list field marked readonly, signalling immutability after construction and matching standard C# convention