format: monomorphise the Storage parsers so local files stay as fast

Every `*_in` core and the read helpers take `file: &S` with
`S: Storage + ?Sized` instead of `&dyn Storage`, and the `&[u8]`
wrappers pass the slice itself, so they compile to a `[u8]` instance:
`as_contiguous()` inlines to `Some(self)` and each structure read is the
slice code's bounds check again, with no indirect call. `&dyn Storage`
still works (`S = dyn Storage`); there is one parser implementation.

Also, so the structure reads cost no more than the slice checks did:
- ObjectHeader::parse_in reads the prefix once (signature included)
  instead of the signature and then the prefix: two reads for a
  one-chunk header instead of three on a range backend;
- the symbol-table node and group B-tree (v1) loops walk their entries
  with chunks_exact over the bytes read, and the node's redundant second
  bounds check is gone (the entries' read is the check, same error);
- a version-1 header's message list is sized from its (capped) count.
Same results and errors; the unit and equivalence tests are unchanged.

New Criterion bench `clawhdf5/benches/local_metadata_bench.rs` over a
400-group version-1 file written by h5py (new fixture
`v1_groups_400.h5`): ObjectHeader::parse, symbol-table nodes, the group
B-tree walk and a facade listing, using only APIs that exist at f2ff2c4
so it builds there for an A/B.

Provisional A/B against f2ff2c4 (busy machine, not for docs): both
builds linked into one binary and timed in alternation, 200 rounds;
median ratio new/old: facade listing -0.5% to -3.5% (was +14%),
ObjectHeader::parse +1% to +2% (was +25%), symbol-table nodes -18%,
group B-tree walk -18%, local-heap names and resolve_group_children
within +-1.5%. An old-vs-old-copy run shows +-2% from code layout alone.

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

crates/clawhdf5-format/src/fixed_array.rs

@@ -92,12 +92,12 @@ impl FixedArrayHeader {
         offset_size: u8,
         length_size: u8,
     ) -> Result<Self, FormatError> {
-        Self::parse_in(&file_data, offset as u64, offset_size, length_size)
+        Self::parse_in(file_data, offset as u64, offset_size, length_size)
     }
 
     /// [`Self::parse`] over any [`Storage`]: one read of the header.
-    pub fn parse_in(
-        file: &dyn Storage,
+    pub fn parse_in<S: Storage + ?Sized>(
+        file: &S,
         offset: u64,
         offset_size: u8,
         length_size: u8,
@@ -174,8 +174,8 @@ pub fn read_fixed_array_chunks(
 /// [`read_fixed_array_chunks`] over any [`Storage`]: one read of the data
 /// block's prefix, one of the whole data block (pages included).
 #[allow(clippy::too_many_arguments)]
-pub fn read_fixed_array_chunks_in(
-    file: &dyn Storage,
+pub fn read_fixed_array_chunks_in<S: Storage + ?Sized>(
+    file: &S,
     header: &FixedArrayHeader,
     dataset_dims: &[u64],
     max_dims: Option<&[u64]>,