Refactor timeout handling in DatabricksSqlHook to use explicit signaling (#62623)

Replace implicit timeout detection based on Timer.is_alive() with explicit
timeout signaling via threading.Event. Timeout classification now checks an
explicit signal set by the timeout callback instead of inferring state from
thread lifecycle behavior.

Preserves existing cancellation semantics and exception types. Unit tests have been adjusted accordingly.

Co-authored-by: Sameer Mesiah <smesiah971@gmail.com>