Fix cargo doc Warnings (#14948)

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# Description
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As an avid `cargo doc` enjoyer I realized we had some doc warnings, so I
fixed them.

After this PR `cargo doc --workspace` should stop throwing warnings.
# User-Facing Changes
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No code changes.

# Tests + Formatting
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- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

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We could add a `cargo doc` CI pipeline but usually running a full `cargo
doc` takes like forever, so maybe we don't want that.

crates/nu-protocol/src/errors/shell_error/io.rs

@@ -256,9 +256,10 @@ impl IoError {
 
     /// Creates a new `IoError` for internal I/O errors with a specific path.
     ///
-    /// This constructor is similar to [`new_internal`] but also includes a file or directory
-    /// path relevant to the error. Use this function in rare cases where an internal error
-    /// involves a specific path, and the combination of path and additional context is helpful.
+    /// This constructor is similar to [`new_internal`](Self::new_internal) but also includes a
+    /// file or directory path relevant to the error.
+    /// Use this function in rare cases where an internal error involves a specific path, and the
+    /// combination of path and additional context is helpful.
     ///
     /// # Examples
     /// ```rust