[executor] No fork test for simulate() — simulation gate correctness against real contract state unverified

[obchain]

PR: #41 (feat/executor: transaction builder + eth_call simulator)
File: crates/charon-executor/src/simulation.rs
Refs #41

Problem

CLAUDE.md safety invariant: "every liquidation transaction passes an eth_call simulation gate before broadcast."

simulation.rs contains one test: simulator_holds_addresses, which asserts that two addresses are stored in a struct. It does not call simulate() at all. There is no test that:

1. Runs simulate() with valid liquidation calldata against a BSC fork — expecting Ok.
2. Runs simulate() with invalid calldata (wrong protocolId, zero repay) — expecting Err.
3. Verifies that an onlyOwner revert is correctly surfaced when sender != owner.
4. Verifies that the gas_limit forwarding (once fixed per the companion issue) gates OOG scenarios.

Without these tests, the gate is structurally present but its correctness against real-world revert conditions is entirely unverified.

Fix

Add fork tests gated behind BSC_FORK_URL env var, following the pattern in crates/charon-protocols/tests/venus_live.rs:

#[tokio::test]
#[ignore = "requires BSC_FORK_URL"]
async fn simulate_valid_liquidation_succeeds() { ... }

#[tokio::test]
#[ignore = "requires BSC_FORK_URL"]
async fn simulate_wrong_sender_fails_onlyowner() { ... }

[obchain]

Resolved in ad042ec on feat/16-executor-builder-and-sim.