[executor] workspace lint policy unenforced in charon-executor — lints.workspace missing

[obchain]

PR: #45 (feat/20-multi-liq-batcher)
Files: Cargo.toml (root, no [workspace.lints]), crates/charon-executor/Cargo.toml (no lints.workspace = true)

The workspace lint policy — forbid(unsafe_code), deny(arithmetic_side_effects), deny(cast_possible_truncation), deny(unwrap_used) — is not declared in the root Cargo.toml [workspace.lints] section and is not inherited by charon-executor. batcher.rs and all other modules in the crate compile without these guards. cargo clippy --workspace does not flag violations in this crate.

Pre-existing gap from PR #41 finding 8. Not resolved in PR #42, #43, or this PR.

Impact: Future arithmetic in batcher.rs (e.g., in profit ranking, chunk indexing) bypasses the deny(arithmetic_side_effects) check. deny(unwrap_used) is not enforced, permitting unwrap() calls that would panic in production.

Fix:

1. Add [workspace.lints] to the root Cargo.toml with the four lint declarations.
2. Add lints.workspace = true to every crate Cargo.toml in the workspace, including charon-executor.
3. Fix any violations that surface after enabling the lints.

Refs #45

[obchain]

Resolved on feat/20-multi-liq-batcher in 5da4129. Root Cargo.toml now carries [workspace.lints.rust] unsafe_code=forbid and [workspace.lints.clippy] arithmetic_side_effects=deny, cast_possible_truncation=deny, unwrap_used=deny. crates/charon-executor/Cargo.toml opts in via [lints] workspace = true. Pre-existing violations in gas.rs and nonce.rs were repaired so the opt-in is viable.