feat(tools): h5rs, pure-Rust HDF5 tools (ls, dump, stat, diff, check)

New workspace crate clawhdf5-tools with one binary, h5rs, built only on the
clawhdf5 facade and clawhdf5-format (no libhdf5, no C):

- ls [-r] [-v] FILE[/path]: h5ls's listing (same text in its first two
  columns) plus the datatype; -v adds address, link count, layout and chunk
  index, chunk size, storage, filters, datatype and attributes.
- dump [--json] [-A] [-p] [-d PATH] FILE: h5dump DDL (byte-identical to
  h5dump 1.14.6 on the test files) or hdf5-json.
- stat FILE: h5stat's object/link/rank/layout/filter/attribute counts, raw
  data and total size.
- diff [-r] [-q] [-d D] [-p R] A B [OBJ1 [OBJ2]]: structural and value
  differences, exit 0/1/2 like h5diff.
- check [--data] FILE: walks every object, parses every message, verifies
  the checksums of every v2+ structure (including the fractal heap blocks
  the library never checks), checks chunk indexes against their datasets
  and raw data for out-of-file or overlapping extents; every problem with
  its address.

Values over --max-bytes are reported, not read; dense-storage heaps are
verified before objects are read from them; panics are caught (exit 3).
Tests compare with h5ls, h5stat, h5dump and h5diff and with h5py's values,
and flip the checksum of every checksummed structure in a v1.14-format file.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-tools/src/cli.rs

@@ -0,0 +1,45 @@
+//! Argument handling and output plumbing shared by the subcommands.
+
+use std::io::Write;
+
+/// Where a subcommand writes: `o` for results, `e` for diagnostics.
+pub struct Out<'a> {
+    pub o: &'a mut dyn Write,
+    pub e: &'a mut dyn Write,
+}
+
+/// The arguments after the subcommand name.
+pub struct Args {
+    cmd: &'static str,
+    rest: std::vec::IntoIter<String>,
+}
+
+impl Args {
+    pub fn new(cmd: &'static str, rest: Vec<String>) -> Self {
+        Self {
+            cmd,
+            rest: rest.into_iter(),
+        }
+    }
+
+    #[allow(clippy::should_implement_trait)]
+    pub fn next(&mut self) -> Option<String> {
+        self.rest.next()
+    }
+
+    /// The value after an option such as `--max-bytes`.
+    pub fn value(&mut self) -> Option<String> {
+        self.rest.next()
+    }
+
+    /// A numeric option value.
+    pub fn number<T: std::str::FromStr>(&mut self) -> Option<T> {
+        self.rest.next().and_then(|s| s.parse().ok())
+    }
+
+    /// Report a usage problem; exit status 2.
+    pub fn usage_error(&self, out: &mut Out, msg: &str, usage: &str) -> std::io::Result<i32> {
+        writeln!(out.e, "h5rs {}: {msg}\n\n{usage}", self.cmd)?;
+        Ok(2)
+    }
+}