feat: introduce SP1_MOONGATE_SERVER_PORT env value as port for moongate-server

[fyInALT]

Motivation

In testing sp1 and op-succinct, we found that when using CUDA proving mode, the Moongate server's default port is set to 3000, which can easily cause port conflicts with other services on the machine. Since many proof service implementations do not actively configure this port parameter.

Solution

we could introduce an environment variable to specify the desired port. For example:

SP1_MOONGATE_SERVER_PORT=13001 SP1_PROVER=cuda RUST_LOG=debug ./target/release/fibonacci-script

This will instruct the Moongate server to use port 13001:

2025-08-07T15:42:59.954343Z DEBUG starting new connection: http://localhost:13001/

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[leruaa]

This can already be done with https://docs.rs/sp1-sdk/5.2.1/sp1_sdk/cuda/builder/struct.LocalMoongateServerCudaProverBuilder.html#method.port:

Something like:

let client = ProverClient::builder()
    .cuda()
    .local()
    .port(13001)
    .build()