feat(gateway)!: impl Stream for Shard

[vilgotf]

Public API change log

• Config no longer stores EventTypeFlags.
• stream::StartRecommendedError was moved to error::StartRecommendedError and it got kind, into_source, and into_parts methods.
• error::ProcessError was removed.
• error::SendError was renamed to ChannelError and its (singular) variant is now named Closed.
• error::ReceiveMessageErrorType now has only four variants (down from 7): Compression, Deserializing, Reconnect, and WebSocket (previously Io).
• parse no longer errors on unknown events.
• the create_ set of functions are now scoped under root.
• create_bucket performs additional input validation and takes correct integer sizes.
• create_range is now create_iterator and takes an iterator instead of a range.
• Added Message::is_close and Message::is_text boolean helpers.
• ConnectionStatus was renamed to ShardState and the Connected variant to Active. Additionally, CloseCode is no longer stored and a few methods were removed.
• Shard::status was renamed to Shard::state.
• Shard::command, Shard::send, and Shard::close now queue themselves like MessageSender and are therefore non-async functions returning ().
• Shard::next_event was replaced by stream::StreamExt::next_event which takes EventTypeFlags as an argument.
• Shard::next_message was replaced by poll_next.

[Gelbpunkt]

From what I could tell this code is indeed now cancellation safe, which is an awesome improvement. Thanks a lot for the PR!

[Gelbpunkt]

Commit message and title should be updated to include a ! to indicate the breaking change. To make writing a changelog easier, I would also like the PR description to mention deserialize_wanted with stream adapters as a replacement for next_event.

[Erk-]

The Shard::stream module was removed.

This should probably have been the stream module.