Cannot impl `std::os::windows::fs::MetadataExt` in stable rust

[Berrysoft]

The 3 methods added in #63010 makes MetadataExt cannot be implemented in stable rust.

error[E0046]: not all trait items implemented, missing: `volume_serial_number`, `number_of_links`, `file_index`
   --> compio-fs\src\metadata\windows.rs:149:1
    |
149 | impl MetadataExt for Metadata {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `volume_serial_number`, `number_of_links`, `file_index` in implementation
    |
    = help: implement the missing item: `fn volume_serial_number(&self) -> Option<u32> { todo!() }`
    = help: implement the missing item: `fn number_of_links(&self) -> Option<u32> { todo!() }`
    = help: implement the missing item: `fn file_index(&self) -> Option<u64> { todo!() }`

The trait should provide default impls for them.

[ChrisDenton]

You're not really meant to implement such extension traits on your own type. They're just used as a mechanism to add platform-specific functions to std types. Nowadays such traits are usually sealed (e.g. OsStrExt, ChildExt, etc) specifically to prevent this.

[the8472]

Might as well seal this one too while it's unimplementable.