websocket/stream: Fix state reset and backport connection tests (#374)

This PR addresses a bug in the WebSocket stream state machine. The
internal state was incorrectly reset to `State::ReadyToSend` upon
receiving `Poll::Pending`. The correct behavior is to retain the
`State::FlushPending` state until the flush operation completes.

Additionally, the following tests were backported from the TCP
connection component:
- yamux_timeout_listener
- yamux_timeout_dialer
- yamux_not_supported_listener
- yamux_not_supported_dialer
- noise_timeout_dialer
- noise_wrong_handshake_listener
- noise_timeout_listener
- noise_not_supported_listener
- noise_not_supported_dialer
- multistream_select_not_supported_listener
- multistream_select_not_supported_dialer

While at it, we had a test guarded by a wrongly named feature flag
`webscocket`, which is now also enabled.

cc @paritytech/networking

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Author: lexnv