ptp: Silence warning about some unused trait methods

These are not used yet but will likely be useful in the future.
Rust 1.79 (nightly) is warning about them being unused.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6601>

subprojects/gstreamer/libs/gst/helpers/ptp/parse.rs

@@ -8,6 +8,8 @@
 //
 // SPDX-License-Identifier: MPL-2.0
 
+#![allow(unused)]
+
 use std::io;
 
 pub trait ReadBytesBEExt: io::Read {