conformance: split out svm/conformance into its own crate #13382

Problem

SVM-related conformance code is growing within the conformance module of the solana-svm crate. Not all of it is related to the solana-svm crate itself, but rather the "SVM" domain.

We should give this stuff its own crate.

Proposed Solution

Extract svm/conformance into its own crate - solana-svm-conformance.

• This new crate should be a resident of the dev-bins workspace.
• This new crate will require crate-type = ["lib", "cdylib"] in its manifest.
• This new crate should be entirely gated under #![cfg(feature = "agave-unstable-api")] like most other Agave crates.
• This new crate should still gate everything protobuf/prost/FFI behind a crate feature, but it should be named ffi instead of conformance, exactly as solana-svm was doing with its conformance feature.
• solana-svm will have no need for its conformance crate feature so it can be removed.
• solana-svm APIs like process_message may have to be made pub under dev-context-only-utils.
• Consumers like programs/sbf will need updating.

Part of #12378