feat: full NFSv4.2 server and client in pure Go

Assisted-by: GLM 5.3 Flash

internal/nfsfs/xattr_stub.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+//go:build !linux && !freebsd
+
+package nfsfs
+
+// GetXattr answers that the backend carries no extended attributes; the
+// platforms without a system xattr interface serve none.
+func (l *Local) GetXattr(h Handle, name string, max int) ([]byte, error) {
+	return nil, ErrXattrNotSupp
+}
+
+// SetXattr answers that the backend carries no extended attributes.
+func (l *Local) SetXattr(h Handle, name string, value []byte, mode uint32) error {
+	return ErrXattrNotSupp
+}
+
+// ListXattr answers that the backend carries no extended attributes.
+func (l *Local) ListXattr(h Handle, max int) ([]string, error) {
+	return nil, ErrXattrNotSupp
+}
+
+// RemoveXattr answers that the backend carries no extended attributes.
+func (l *Local) RemoveXattr(h Handle, name string) error {
+	return ErrXattrNotSupp
+}