Examine, how to properly cancel 1 task within anyio.TaskGroup

[dolamroth]

No description provided.

[dolamroth]

May be related to:
agronholm/anyio#374
agronholm/anyio#496

From the discussion, it seems, that cancelling just one task within CancelScope may be not the desired behavior within anyio/trio paradigm.

However, since a cancellation may be delivered from non-user's code (i.e. calling library, that creates orphan tasks), such calls must be incapsulated with shielding cancel scope by user. This should be mentioned in the docs about websockets.

[dolamroth]

The task handler can actually be obtained, by calling task_group._spawn instead of task_group.start_soon, albeit not recommended.

There is also a trick with passing an inner cancel_scope outside from task: https://stackoverflow.com/a/60675826 (anyio has same API)

[dolamroth]

In websocket endpoint, we should pass task_id from outer scope (on_release), so that user can re-define it and have possibility to call task_group.start instead of task_group.start_soon