prove-sbf and prove-slot ignore --output and discard generated proofs

[blacks1ne]

Description

Both Solana-facing proving binaries accept a documented --output argument but never use it:

• crates/sbf/src/bin/prove-sbf.rs stores the value in _output_path at lines 34 and 42.
• crates/sbf/src/bin/prove-slot.rs stores the value in _output_path at lines 149 and 168.

Neither binary serializes a proof or writes a file. Proofs are only verified in memory and then dropped. This contradicts the README, which documents sbf_proof.bin and slot_proof.bin output files.

Reproduction

After resolving the workspace's missing trusted-setup build blocker:

cargo run --release --bin prove-sbf -- \
  --asm $'mov64 r0, 1\nexit' \
  --output /tmp/sbf-proof.bin

test -e /tmp/sbf-proof.bin

The prover reports success, but the requested file is not created. Static inspection shows the same behavior in prove-slot.

Expected behavior

• prove-sbf --output PATH writes the verified RecursiveProof to PATH.
• prove-slot --output PATH writes a documented slot/transaction proof bundle to PATH, or rejects the option until a bundle format is defined.
• Write failures produce a non-zero exit status.

Suggested resolution

Use the canonical RecursiveProof::to_bytes() encoding for individual proofs. For slot output, define a versioned container that associates each proof with its transaction signature/index and records failures or skipped instructions.

Add CLI integration tests that pass a temporary output path, decode the artifact, and verify it.