feat: clean up NetworkProver environment variables

[leruaa]

Motivation

We need to remove environment variables as they make SP1 difficult to use in a prod environment.

Solution

I added a NetworkProverClientBuilder builder that handle the equivalent of the following environment variables:

• SKIP_SIMULATION
• SP1_PRIVATE_KEY
• PROVER_NETWORK_RPC

The environment variables are still used in ProverClient::new() for backward compatibility.

I only added a builder for the network builder as there is nothing to build for other provers.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[github-actions]

SP1 Performance Test Results

Branch: aurelien/gro-272-use-builder-pattern-for-sdk
Commit: d2e073b
Author: leruaa

program	cycles	execute (mHz)	core (kHZ)	compress (KHz)	time	success
fibonacci	11291	0.18	2.73	0.46	25s	✅
ssz-withdrawals	2757356	16.56	123.13	34.98	1m19s	✅
tendermint	12593597	6.72	270.32	101.09	2m6s	✅