feat(tls): futures compat

[Berrysoft]

This PR ports the code of tokio-native-tls for the native-tls and py-openssl backend. There might be some redundant code...

As it is built on top of AsyncStream, the TlsStream is futures-compatible now. The downside is that it will always require Box::pin.

[Copilot]

Pull request overview

This PR refactors compio-tls’s TlsStream implementation to be futures-compatible by adapting TLS backends (native-tls and py-openssl) to futures_util::AsyncRead/AsyncWrite via compio_io::compat::AsyncStream, and routing compio’s async IO through those futures traits.

Changes:

• Replace SyncStream-based native-tls and py-openssl handling with futures-compatible TLS stream wrappers built around AsyncStream + Pin<Box<...>>.
• Add new native backend module ported from tokio-native-tls, and heavily rework the py-openssl backend to use a similar polling/context-pointer approach.
• Update connector/acceptor implementations and feature flags to depend on futures-util where required.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
compio-tls/src/stream.rs	Reworks TlsStream to delegate IO through futures AsyncRead/AsyncWrite and adds vectored-write support.
compio-tls/src/py_ossl.rs	Replaces the previous drive-loop implementation with a futures-style polling adapter around SslStream.
compio-tls/src/native.rs	New native-tls futures adapter ported from tokio-native-tls.
compio-tls/src/adapter.rs	Updates connector/acceptor to construct pinned AsyncStream and use the new backend wrappers.
compio-tls/src/maybe.rs	Moves negotiated_alpn into a bounded impl block consistent with new TlsStream bounds.
compio-tls/src/lib.rs	Wires in the new native module behind the native-tls feature.
compio-tls/Cargo.toml	Adds futures-util as a feature dependency for native-tls and py-openssl backends.

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[George-Miao]

LGTM

[fantix]

LGTM and go ahead with merging and all, I'll try adapting my kTLS-compat draft PR this weekend and submit tweaks if needed.