State Management

[Totodore]

Currently there is no global state management for socketioxide so it is quite frustrating to manage state.
Most of the time it is needed to make a global OnceCell or something like that and then getting the state from the Cell each time it is required.

Because of the current architecture with the imbricated closures it is not possible to adopt the "Axum" way of managing state which is having only one typed field on handlers and then using a State extractor to extract it. It has many advantages because it allows to have State type checking at compilation and it is quite efficient.

The remaining way of achieving state management in socketioxide is to have either one dynamic OnceCell or a TypeMap stored in the Client and an extractor that extract the corresponding data. In case of failure it would not call the handler and a tracing error would be logged.

Things to do are :

• Add a state module and a state struct with a dynamic TypeMap but only with creation fn (no mut ref). (behind a feature flag)
• Add a field in the client module for the state struct (behind feature flag)
• Pass a state reference to every handlers
• Create a State extractor that would extract a given state from the TypeMap