feat(socketio): Async adapter

[Totodore]

Motivation

Transform the Adapter trait to return impl Future + Send so that it is possible to implement adapters with other systems (redis, mongo, ...).

Solution

• The Adapter returns impl Future + Send for all the methods that may need to communicate remotely (e.g emit, emit_with_ack on the BroadcastOperators and SocketIo structs).
• The base adapter logic has been moved to the socketioxide_core trait as well as some error types. So that new adapters only need to depends on socketioxide_core.
• Packet and AckError implement Serialize in order to send them to remote nodes.
• ParserError is now simply a wrapper around a Box<impl StdError> so that it is easy to impl serde on it. Therefore the DecodeError and EncodeError GAT have been removed.
• A new adapter State GAT allow any Adapter implementors to share a common state between all adapters of a node. It can be useful to share a connection to a remote server (redis, mongo, ...).
• A new AckStream GAT allow the adapter to merge a stream from the local node with a remote stream of acknowledgments.

Remaining questions/issues:

• Find a solution to initialize each namespace. Currently namespaces are initialized through a spawned task. But this leads to failed tests and the user can't get the error if the initialization failed.

To do:

• Update documentation on operators. Some socket methods are sync and local whereas the same method is async on BroadcastOperators.

[github-advanced-security]

clippy found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.