feat: Create endpoint manager for websockets

[shahnami]

Summary

https://linear.app/openzeppelin-development/issue/PLAT-6659/refactor-rpc-calls-to-use-substrate-client-with-websocket

• Moves http and websocket related logic into their own folders
• Creates websocket specific endpoint manager and transport
• Creates midnight specific websocket client
• Adds integration tests for websockets

TODO (in follow up PRs):

• Replace HTTP Midnight client with WS Midnight client entirely
• Replace midnight_jsonBlock and midnight_decodeEvents RPC calls with substrate client calls
• Update documentation

Testing Process

Checklist

• Add a reference to related issues in the PR description.
• Add unit tests if applicable.
• Add integration tests if applicable.
• Add property-based tests if applicable.
• Update documentation if applicable.

[NicoMolinaOZ]

Do we need this to maintain consistency with other transport implementations?

[shahnami]

That's right, it implements BlockchainTransport where we only need get_current_url and send_raw_request.

We don't need retry policy logic and update_endpoint_manager because our websocket implementwtion doesn't have a middleware client, as opposed to http implementation, which has the reqwest middleware client. Mainly because of how connections are handled in http vs websockets.

As you can see, we don't actually have a client associated in the endpoint manager for ws to update. It simply manages rotation based on weights. Whereas for http it's a bit more complex, where we can configure different retry strategies based on error codes etc.. I hope that makes sense.

[NicoMolinaOZ]

Makes sense! thanks for the explanation Nami!

[NicoMolinaOZ]

LGTM!