Enable `cargo prove build` to handle arbitrary Rust flags

[ratankaliani]

All Rust feature flags should work with cargo prove build.

Currently, we only support --ignore-rust-version.

https://github.com/succinctlabs/sp1/blob/e413e82e86ef97007094d830da1d3b278075a4bc/cli/src/build.rs#L17-L24