`DiscordAdapter.disconnect()` cancelled the bot task before tearing down voice
clients. `leave_voice_channel()` ends in `await vc.disconnect()`, and discord.py
sends a voice state update over the main gateway websocket and then waits for the
voice socket to close. The bot task is the loop running that gateway connection,
so cancelling it first left the handshake with no transport: it could never
complete and blocked until the caller's shutdown timeout fired.
The effect was a fixed ~5s penalty on every shutdown with a voice connection
open, ending in "discord disconnect timed out after 5.0s - forcing continue",
with the voice disconnect abandoned rather than completed.
Measured on a live gateway with a voice connection open in both cases:
before: timed out after 5.0s, all adapters disconnected at +5.29s
after: discord disconnected (0.12s), all adapters disconnected at +0.46s
Moving the voice-cleanup loop above `_cancel_bot_task()` preserves the
zombie-client protection its comment describes: the bot task is still cancelled
before `client.close()`, just after voice teardown rather than before it. Voice
teardown is the one step that still requires a live gateway.
Adds a regression test asserting the ordering. It fails on the previous ordering
at index 1 with `cancel_bot_task != leave_voice_channel:111`.
Fixes#76044
e6f1d613b6