lint: upgrade perfectionist to 0.0.0-rc.21

`0.0.0-rc.21` replaces `import_grouping_mismatch`'s `separate_reexports`
boolean with a mandatory `reexports` enum
(KSXGitHub/perfectionist#335), implementing the alias-vs-submodule
re-export split requested in #443.

- Set `reexports = "split"` so submodule re-exports
  (`pub use child::Item;`) sit above alias re-exports
  (`pub use Item as Alias;`) in their own blank-separated blocks.
  Reorganize the three modules that mix both kinds (`data_tree`,
  `hardlink_list`, `link_path_list`).
- Update `CONTRIBUTING.md` to describe the split layout.

https://claude.ai/code/session_016ZyYFnzSv876usUHLEX4qe

Author: claude

CONTRIBUTING.md

@@ -39,32 +39,30 @@ Automated tools enforce formatting (`cargo fmt`), linting (`cargo clippy`), and
 Two `perfectionist` rules govern imports automatically:
 
 - `perfectionist::import_granularity_mismatch`, configured for the `module` style, controls how items are merged within each `use` statement. Items from the same module are merged into a single braced `use` statement, while each module keeps its own `use` statement rather than collapsing an entire crate into one nested-braces statement.
-- `perfectionist::import_grouping_mismatch`, configured for the `single_block` style, controls how `use` statements are partitioned into blocks. Private imports sit in one contiguous block with no blank lines between them, while `pub use` re-exports are pulled into their own leading block, separated by a blank line (the rule's default `separate_reexports = true`).
+- `perfectionist::import_grouping_mismatch`, configured for the `single_block` style with `reexports = "split"`, controls how `use` statements are partitioned into blocks. Private imports sit in one contiguous block with no blank lines between them. `pub use` re-exports lead, split into two blank-separated sub-blocks: submodule re-exports (a multi-segment path such as `pub use child::Item;`) above alias re-exports (a single-segment path such as `pub use Item as Alias;`).
 
 Import ordering within the block is enforced separately by `cargo fmt`.
 
 Imports gated by a platform or feature attribute such as `#[cfg(unix)]` are kept in their own block after the main imports, separated by a blank line. Under `single_block` the rule recognizes this trailing `#[cfg]` block automatically through its default `cfg_block_handling = "trailing"`, so no manual exception is required.
 
 ```rust
-pub use sub::Sub;
+pub use iter::Iter;
+pub use reflection::Reflection;
+
+pub use Reflection as ListReflection;
 
-use crate::args::{Args, Quantity, Threads};
-use crate::bytes_format::BytesFormat;
 use crate::size;
-use clap::Parser;
-use pipe_trait::Pipe;
-use std::io::stdin;
-use std::time::Duration;
+use std::path::PathBuf;
 
 #[cfg(unix)]
-use crate::get_size::{GetBlockCount, GetBlockSize};
+use std::os::unix::fs::MetadataExt;
 ```
 
 ### Module Organization
 
 The flat file pattern (`module.rs` rather than `module/mod.rs`) is enforced by `clippy::mod_module_files`, enabled in `Cargo.toml`. Earlier releases relied on a `perfectionist::flat_module_pattern` rule; `perfectionist` `0.0.0-rc.19` removed it in favor of the equivalent Clippy lint. In addition to that requirement, follow these conventions:
 
-- List `pub mod` declarations first, then the `pub use` re-exports in their own group, then the private `use` block, then the remaining items. `perfectionist::import_grouping_mismatch` (`separate_reexports`) keeps the re-exports in a block of their own above the private imports, and `cargo fmt` sorts within each block.
+- List `pub mod` declarations first, then the `pub use` re-exports, then the private `use` block, then the remaining items. `perfectionist::import_grouping_mismatch` (`reexports = "split"`) keeps re-exports above the private imports, split into a submodule-re-export block and an alias-re-export block, and `cargo fmt` sorts within each block.
 - Use `pub use` to re-export key types at the module level for convenience.
 
 ```rust

dylint.toml

@@ -1,6 +1,6 @@
 [workspace.metadata.dylint]
 libraries = [
-    { git = "https://github.com/KSXGitHub/perfectionist", tag = "0.0.0-rc.20" },
+    { git = "https://github.com/KSXGitHub/perfectionist", tag = "0.0.0-rc.21" },
 ]
 
 [perfectionist]
@@ -30,6 +30,7 @@ style = "module"
 
 ["perfectionist::import_grouping_mismatch"]
 style = "single_block"
+reexports = "split"
 
 ["perfectionist::impure_macro_arguments"]
 deny_extra = ["debug_assert_op", "debug_assert_op_expr"]

src/data_tree.rs

@@ -1,8 +1,9 @@
 pub mod reflection;
 
-pub use Reflection as DataTreeReflection;
 pub use reflection::Reflection;
 
+pub use Reflection as DataTreeReflection;
+
 use super::size;
 
 /// Disk usage data of a filesystem tree.

src/hardlink/hardlink_list.rs

@@ -2,12 +2,13 @@ pub mod iter;
 pub mod reflection;
 pub mod summary;
 
-pub use Reflection as HardlinkListReflection;
-pub use Summary as SharedLinkSummary;
 pub use iter::Iter;
 pub use reflection::Reflection;
 pub use summary::Summary;
 
+pub use Reflection as HardlinkListReflection;
+pub use Summary as SharedLinkSummary;
+
 use crate::device::DeviceNumber;
 use crate::hardlink::LinkPathList;
 use crate::inode::InodeNumber;

src/hardlink/link_path_list.rs

@@ -1,10 +1,11 @@
 mod iter;
 mod reflection;
 
-pub use Reflection as LinkPathListReflection;
 pub use iter::Iter;
 pub use reflection::Reflection;
 
+pub use Reflection as LinkPathListReflection;
+
 use std::path::PathBuf;
 
 /// List of different hardlinks to the same file.