fix: refuse numeric types with unusually many unused bits in v1 headers

libhdf5 1.14.4+ treats an integer, float or bit field wider than a byte
whose precision and offset leave more than half its bits unused as
corruption when the type sits in a header without a checksum (version 1),
unless the file is opened with H5Pset_relax_file_integrity_checks
(H5T_is_numeric_with_unusual_unused_bits). clawhdf5 read such types,
e.g. a 3-bit integer in 4 bytes (cve-2024-29162) or a 32-bit float in
65525 bytes (cve-2024-32614, tmisc38a.h5).

New Datatype::check_unused_bits (recursive) and Datatype::parse_in_header,
which applies it for version-1 headers. Dataset datatypes (facade File,
LazyFile, MmapFile; clawhdf5-io VOL, MPI VOL, async reader; the
conformance probe) and compact attributes in version-1 headers use it.

Conformance (cached corpus, tank): 570 ok, unchanged; cve-2024-29162,
cve-2024-32614 and tmisc38a.h5 now refuse the object h5py refuses, and
tmisc38b.h5 / unknown-1.h5 now fail with libhdf5's reason.

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

conformance/probe/src/main.rs

@@ -313,7 +313,7 @@ impl<'a> Ctx<'a> {
         let dtb = self
             .payload(h, MessageType::Datatype)?
             .ok_or("MissingMessage(Datatype)")?;
-        Datatype::parse(&dtb).map_err(e)?;
+        Datatype::parse_in_header(&dtb, h.version).map_err(e)?;
         Ok(())
     }
 
@@ -321,7 +321,7 @@ impl<'a> Ctx<'a> {
         let dtb = self
             .payload(h, MessageType::Datatype)?
             .ok_or("MissingMessage(Datatype)")?;
-        let (dt, _) = Datatype::parse(&dtb).map_err(e)?;
+        let (dt, _) = Datatype::parse_in_header(&dtb, h.version).map_err(e)?;
         rec.insert("dtype".into(), Value::String(dtype_str(&dt)));
         let dsb = self
             .payload(h, MessageType::Dataspace)?