[codex] Preserve typed SNOS RPC errors

[prkpndy]

What changed

• preserve typed provider, proof, and state-update errors instead of collapsing them into generic strings
• expose structured join/state/proof errors from generate-pie so downstream callers can distinguish retryable RPC failures from deterministic execution failures

Why

Orchestrator needs reliable SNOS error typing to avoid fail-fasting on intermittent RPC and proof-fetch failures while still failing immediately on deterministic Cairo execution errors.

Impact

• SNOS callers can now inspect RPC/proof/state-update failures structurally
• downstream retry logic can key off real error variants rather than string parsing

Validation

• cargo clippy --workspace --all-features --tests --no-deps -- -D warnings
• cargo fmt