Mautrix

* *(bridge, crypto)* Fixed key sharing trust checker not resolving cross-signing
signatures when minimum trust level is set to cross-signed.

* *(crypto)* Added cache checks to prevent invalidating group session when the
server sends a duplicate member event in /sync.
* *(util.proxy)* Fixed `min_wait_seconds` behavior and added `max_wait_seconds`
and `multiply_wait_seconds` to `proxy_with_retry`.

* *(util.proxy)* Added utility for dynamic proxies (from mautrix-instagram/facebook).
* *(types)* Added default value for `upload_size` in `MediaRepoConfig` as the
field is optional in the spec.
* *(bridge)* Changed ghost invite handling to only process one per room at a time
(thanks to [maltee1] in [132]).

[132]: https://github.com/mautrix/python/pull/132

* *(types)* Changed `set_thread_parent` to inherit the existing thread parent
if a `MessageEvent` is passed, as starting threads from a message in a thread
is not allowed.
* *(util.background_task)* Added new utility for creating background tasks
safely, by ensuring that the task is not garbage collected before finishing
and logging uncaught exceptions immediately.

* *(bridge)* Bumped default timeouts for decrypting incoming messages.

* *(util.async_body)* Added utility for reading aiohttp response into a bytearray
(so that the output is mutable, e.g. for decrypting or encrypting media).
* *(client.api)* Fixed retry loop for MSC3870 URL uploads not exiting properly
after too many errors.