refactor(ws)!: futures compat

[Berrysoft]

This PR uses async-tungstenite to simplify the code, and provide first-class futures compat.

[Copilot]

Pull request overview

Refactors compio-ws to build on async-tungstenite instead of manually driving tungstenite, aiming to provide first-class futures Sink/Stream compatibility and simplify buffering/handshake logic across plain and TLS connections.

Changes:

• Replaces the custom SyncStream-based WebSocket implementation (and the separate compat wrapper) with an async_tungstenite::WebSocketStream-backed WebSocketStream that implements futures_util::Sink/Stream.
• Reworks TLS helpers to wrap streams via compio_io::compat::AsyncStream and adds *_compat entrypoints in compio-tls for passing pre-configured AsyncStreams.
• Updates features/examples/tests to match the new API and removes the old io-compat feature path for websockets.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
compio/Cargo.toml	Adjusts feature wiring for io-compat/tls now that compio-ws changes its compat/TLS surface.
compio-ws/Cargo.toml	Adds async-tungstenite, reshapes features (introduces tls), updates example gating.
compio-ws/src/lib.rs	Major refactor: new WebSocketStream built on async-tungstenite with Sink/Stream impls.
compio-ws/src/tls.rs	Updates TLS wrapping to use AsyncStream limits and new connector APIs; changes return types.
compio-ws/tests/websocket.rs	Updates compat test to use direct Sink/Stream behavior without the old compat wrapper.
compio-ws/examples/ws_split.rs	Switches split example to ws.split() on the native Sink/Stream impl.
compio-ws/src/compat.rs	Removes the old custom futures-compat wrapper implementation.
compio-tls/src/maybe.rs	Adds new_plain_compat(AsyncStream<...>) constructor.
compio-tls/src/adapter.rs	Adds connect_compat/accept_compat to accept pre-configured AsyncStream.
compio-io/src/compat/async_stream.rs	Adds AsyncStream::with_limits constructor.

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[George-Miao]

LGTM