Add support for kTLS

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

common/badtls/registry_utls.go

@@ -0,0 +1,56 @@
+//go:build go1.25 && !without_badtls
+
+package badtls
+
+import (
+	"net"
+	"unsafe"
+
+	N "github.com/sagernet/sing/common/network"
+
+	"github.com/metacubex/utls"
+)
+
+func init() {
+	methodRegistry = append(methodRegistry, func(conn net.Conn) (unsafe.Pointer, *Methods, bool) {
+		var pointer unsafe.Pointer
+		if uConn, loaded := N.CastReader[*tls.Conn](conn); loaded {
+			pointer = unsafe.Pointer(uConn)
+		} else if uConn, loaded := N.CastReader[*tls.UConn](conn); loaded {
+			pointer = unsafe.Pointer(uConn.Conn)
+		} else {
+			return nil, nil, false
+		}
+		return pointer, &Methods{
+			readRecord:                 utlsReadRecord,
+			handlePostHandshakeMessage: utlsHandlePostHandshakeMessage,
+			writeRecordLocked:          utlsWriteRecordLocked,
+
+			setErrorLocked:   utlsSetErrorLocked,
+			decrypt:          utlsDecrypt,
+			setTrafficSecret: utlsSetTrafficSecret,
+			explicitNonceLen: utlsExplicitNonceLen,
+		}, true
+	})
+}
+
+//go:linkname utlsReadRecord github.com/metacubex/utls.(*Conn).readRecord
+func utlsReadRecord(c unsafe.Pointer) error
+
+//go:linkname utlsHandlePostHandshakeMessage github.com/metacubex/utls.(*Conn).handlePostHandshakeMessage
+func utlsHandlePostHandshakeMessage(c unsafe.Pointer) error
+
+//go:linkname utlsWriteRecordLocked github.com/metacubex/utls.(*Conn).writeRecordLocked
+func utlsWriteRecordLocked(hc unsafe.Pointer, typ uint16, data []byte) (int, error)
+
+//go:linkname utlsSetErrorLocked github.com/metacubex/utls.(*halfConn).setErrorLocked
+func utlsSetErrorLocked(hc unsafe.Pointer, err error) error
+
+//go:linkname utlsDecrypt github.com/metacubex/utls.(*halfConn).decrypt
+func utlsDecrypt(hc unsafe.Pointer, record []byte) ([]byte, uint8, error)
+
+//go:linkname utlsSetTrafficSecret github.com/metacubex/utls.(*halfConn).setTrafficSecret
+func utlsSetTrafficSecret(hc unsafe.Pointer, suite unsafe.Pointer, level int, secret []byte)
+
+//go:linkname utlsExplicitNonceLen github.com/metacubex/utls.(*halfConn).explicitNonceLen
+func utlsExplicitNonceLen(hc unsafe.Pointer) int