Add support for kTLS

Reference: https://gitlab.com/go-extension/tls

common/ktls/ktls_read_wait.go

@@ -0,0 +1,41 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && go1.25 && !without_badtls
+
+package ktls
+
+import (
+	"github.com/sagernet/sing/common/buf"
+	N "github.com/sagernet/sing/common/network"
+)
+
+func (c *Conn) InitializeReadWaiter(options N.ReadWaitOptions) (needCopy bool) {
+	c.readWaitOptions = options
+	return false
+}
+
+func (c *Conn) WaitReadBuffer() (buffer *buf.Buffer, err error) {
+	c.rawConn.In.Lock()
+	defer c.rawConn.In.Unlock()
+	for c.rawConn.Input.Len() == 0 {
+		err = c.readRecord()
+		if err != nil {
+			return
+		}
+	}
+	buffer = c.readWaitOptions.NewBuffer()
+	n, err := c.rawConn.Input.Read(buffer.FreeBytes())
+	if err != nil {
+		buffer.Release()
+		return
+	}
+	buffer.Truncate(n)
+	if n != 0 && c.rawConn.Input.Len() == 0 && c.rawConn.Input.Len() > 0 &&
+		c.rawConn.RawInput.Bytes()[0] == recordTypeAlert {
+		_ = c.rawConn.ReadRecord()
+	}
+	c.readWaitOptions.PostReturn(buffer)
+	return
+}