[submit] Submitter returns anyhow::Error — pipeline cannot route Timeout vs RpcRejected vs ConnectionLost

[obchain]

Refs #44

File: crates/charon-executor/src/submit.rs

Problem

submit() returns anyhow::Result. The pipeline must distinguish:

• Timeout: resync nonce, drop opportunity, try next opportunity
• RpcRejected (revert/bad nonce/bad signature): drop opportunity, do NOT resync
• ConnectionLost: reinitialise submitter, retry next tick

With anyhow these collapse to a string. Same recurring issue as PR #41 finding 6 (#163), PR #43 finding 9 (#187).

Fix

Define structured error in submit.rs:

#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum SubmitError {
    #[error("submission timed out after {0:?}")]
    Timeout(std::time::Duration),
    #[error("rpc rejected: {0}")]
    RpcRejected(String),
    #[error("connection lost: {0}")]
    ConnectionLost(#[source] alloy::transports::TransportError),
    #[error("insecure scheme: {0}")]
    InsecureScheme(String),
}

Change submit() to return Result<TxHash, SubmitError>.

[obchain]

Addressed in commits d62d045 and e4170dc on feat/19-private-rpc-submit.