Converge config_ktls_{client,server} bounds to AsRawFd + AsyncRead + Unpin

The two config functions (in version 6.0.2) have identical bodies but inconsistent, over-constrained bounds:

config_ktls_server:   IO: AsRawFd + AsyncRead + AsyncReadReady + AsyncWrite + Unpin
config_ktls_client:   IO: AsRawFd + AsyncRead + AsyncWrite + Unpin

Neither body uses AsyncWrite or AsyncReadReady. The only IO-touching operations are:

• drain(&mut stream) — needs AsyncRead + Unpin
• setup_inner(io.as_raw_fd(), ...) — needs AsRawFd
• KtlsStream::new(io, drained) — needs AsRawFd

AsyncReadReady is never invoked inside either function (the only call site is CorkStream::poll_read_ready).

Proposal: converge both to the minimal set the bodies require:

where IO: AsRawFd + AsyncRead + Unpin,

This is a backward-compatible loosening.

In my use case, I have a wrapping IO type that impls AsRawFd + AsyncRead + Unpin but not AsyncReadReady can be passed to config_ktls_client today but is rejected by config_ktls_server purely on the redundant bound.

If AsyncReadReady was meant to guarantee the returned KtlsStream<IO> is usable as AsyncRead, that bound already lives on impl AsyncRead for KtlsStream<IO>. Maybe there is no need to duplicate it on the config function, and not on the client/server asymmetrically.

Locate config_ktls_client and config_ktls_server in the version 6.0.2 source and compare their generic bounds with the operations used in each body. Check the existing test suite and verify that both functions accept an IO type implementing AsRawFd, AsyncRead, and Unpin without the redundant bounds; done means the project still builds and tests pass.