Fix stderr from Lest not emitting before process is closed

# Context

- When running the Lest "binary" and an error occurs, the error written to `stderr` is not fully emitted before the process terminates and Lest exits
- This makes it impossible to debug issues

# Scope

todo

# Acceptance criteria

- When calling Lest via the JS "binary", and it encounters a Lua error while trying to run tests, the error is emitted to the console