Fix the snake_case helper that replaces an inline copy

An AI agent added an inline to_snake helper to your Python service and used it in three endpoints. It split at every capital letter, so HTTPStatus became h_t_t_p_status, and the service already had a casing helper the agent never looked for. You are replacing both with one canonical helper that understands acronyms.

An assistant wrote to_snake_case(name). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• name: an identifier in any casing style.
• Return it in snake_case: lowercase words joined by _.

Rules the tests check:

• _, - and a space are separators. Each one becomes _.
• Write each uppercase ASCII letter A to Z in lowercase. If it is not the first character, put a _ before it when either of these holds:
  • the character before it is a lowercase ASCII letter or a digit 0 to 9
  • the character before it is an uppercase ASCII letter, and the character after it is a lowercase ASCII letter. This way the last capital of an acronym starts the next word.
• Every other character is copied as it is.
• Finally, collapse every run of _ into a single _, and remove any _ at the start or the end.