Decomposing hot-path modules into focused submodules

Signed-off-by: Alexey <247128645+axkurcom@users.noreply.github.com>

src/proxy/relay/io/combined.rs

@@ -0,0 +1,61 @@
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+// ============= CombinedStream =============
+
+/// Combines separate read and write halves into a single bidirectional stream.
+///
+/// `copy_bidirectional` requires `AsyncRead + AsyncWrite` on each side,
+/// but the handshake layer produces split reader/writer pairs
+/// (e.g. `CryptoReader<FakeTlsReader<OwnedReadHalf>>` + `CryptoWriter<...>`).
+///
+/// This wrapper reunifies them with zero overhead — each trait method
+/// delegates directly to the corresponding half. No buffering, no copies.
+///
+/// Safety: `poll_read` only touches `reader`, `poll_write` only touches `writer`,
+/// so there's no aliasing even though both are called on the same `&mut self`.
+pub(in crate::proxy::relay) struct CombinedStream<R, W> {
+    reader: R,
+    writer: W,
+}
+
+impl<R, W> CombinedStream<R, W> {
+    pub(in crate::proxy::relay) fn new(reader: R, writer: W) -> Self {
+        Self { reader, writer }
+    }
+}
+
+impl<R: AsyncRead + Unpin, W: Unpin> AsyncRead for CombinedStream<R, W> {
+    #[inline]
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.get_mut().reader).poll_read(cx, buf)
+    }
+}
+
+impl<R: Unpin, W: AsyncWrite + Unpin> AsyncWrite for CombinedStream<R, W> {
+    #[inline]
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.get_mut().writer).poll_write(cx, buf)
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.get_mut().writer).poll_flush(cx)
+    }
+
+    #[inline]
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.get_mut().writer).poll_shutdown(cx)
+    }
+}