refactor: make websocket gateway interface type safe

[francescovallone]

# Problem

Right now, the class WebSocketGateway interface uses dynamic in both the onMessage and send methods. This refactor aims to remove the dynamic typing in the data argument in the methods, providing a type-safe interface when sending and receiving messages.

This refactor will also make moving to the new web_socket library easier. (#110)

Analysis

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Solution

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