CodecBuilder::protocol

[rukai]

Pulled out of #1490 but adjusted a bit to use MessageType instead of ProtocolType which will be deleted.

This better abstracts our ability to retrieve the protocol type from a codec builder.
Previously we could only get a string used for websockets.
But now we get an enum that we can convert into the websockets string or use for other purposes.

[github-actions]

0 benchmark regressed. 2 benchmark improved. Please check the benchmark workflow logs for full details: https://github.com/shotover/shotover-proxy/actions/runs/7984440539

Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) high mild
  3 (3.00%) high severe
kafka_codec/decode_request_list_offsets_drop
                        time:   [250.10 ns 251.12 ns 252.40 ns]
                        change: [-28.407% -25.479% -22.328%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  5 (5.00%) low severe
  1 (1.00%) low mild
kafka_codec/encode_request_list_offsets
                        time:   [552.61 ns 562.03 ns 571.35 ns]
                        change: [-28.323% -24.961% -21.331%] (p = 0.00 < 0.05)
                        Performance has improved.