Mirror _message_thread_id_for_typing() with _message_thread_id_for_send():
both now map the General forum topic (thread id "1") to None upfront.
That removes the need for the retry-without-thread fallback in send_typing()
entirely — if _message_thread_id_for_typing() returns a non-None value, it's
a real user-created topic and falling back to the root chat is never correct.
If Telegram rejects the typing action (e.g. topic deleted mid-session), we
swallow it at debug level instead of bleeding the indicator into All Messages.
Updates the General-topic typing regression test to assert the new single-call
contract.
d5357f816d