ANSI sequences for the names of tracing span variables even if color logging is disabled

<img width="1915" height="95" alt="Image" src="https://github.com/user-attachments/assets/b663d0ff-5b90-4247-a244-10afa463ab0f" />

`block_number` is fine (directly associated with the event) but `contract_address` looks bad (associated with the span).