fix(docs): use raw URLs for MetadataExt links to avoid Windows doc errors

std::os::unix::fs::MetadataExt does not exist on Windows, so rustdoc
path links to it cause compilation errors. Use raw doc.rust-lang.org
URLs instead, matching the style used before this PR.

https://claude.ai/code/session_01QP9wZyoZcGmJsEsA66ZRok

Author: claude

src/hardlink/hardlink_list.rs

@@ -75,8 +75,9 @@ impl<Size> HardlinkList<Size> {
 
 /// Error that occurs when a different size was detected for the same [`ino`] and [`dev`].
 ///
-/// [`ino`]: std::os::unix::fs::MetadataExt::ino
-/// [`dev`]: std::os::unix::fs::MetadataExt::dev
+/// <!-- Should have been `std::os::unix::fs::MetadataExt::{ino,dev}` but it would error on Windows -->
+/// [`ino`]: https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.ino
+/// [`dev`]: https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.dev
 #[derive(Debug, Display, Error)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[display(bound(Size: Debug))]
@@ -90,9 +91,10 @@ pub struct SizeConflictError<Size> {
 
 /// Error that occurs when a different [`nlink`] was detected for the same [`ino`] and [`dev`].
 ///
-/// [`nlink`]: std::os::unix::fs::MetadataExt::nlink
-/// [`ino`]: std::os::unix::fs::MetadataExt::ino
-/// [`dev`]: std::os::unix::fs::MetadataExt::dev
+/// <!-- Should have been `std::os::unix::fs::MetadataExt::{nlink,ino,dev}` but it would error on Windows -->
+/// [`nlink`]: https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.nlink
+/// [`ino`]: https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.ino
+/// [`dev`]: https://doc.rust-lang.org/std/os/unix/fs/trait.MetadataExt.html#tymethod.dev
 #[derive(Debug, Display, Error)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[display(