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/superblock.rs

@@ -166,13 +166,13 @@ impl Superblock {
         file_data: &[u8],
         signature_offset: usize,
     ) -> Result<u64, FormatError> {
-        self.refresh_eof_in(&file_data, signature_offset as u64)
+        self.refresh_eof_in(file_data, signature_offset as u64)
     }
 
     /// [`Self::refresh_eof`] over any [`Storage`].
-    pub fn refresh_eof_in(
+    pub fn refresh_eof_in<S: Storage + ?Sized>(
         &mut self,
-        file: &dyn Storage,
+        file: &S,
         signature_offset: u64,
     ) -> Result<u64, FormatError> {
         let refreshed = Superblock::parse_in(file, signature_offset)?;
@@ -233,13 +233,16 @@ impl Superblock {
     /// [`FormatError::UserBlockNotStripped`] because the addresses in the
     /// returned superblock would otherwise be applied to the wrong bytes.
     pub fn parse(data: &[u8], signature_offset: usize) -> Result<Superblock, FormatError> {
-        Self::parse_in(&data, signature_offset as u64)
+        Self::parse_in(data, signature_offset as u64)
     }
 
     /// [`Self::parse`] over any [`Storage`]: one read of the first
     /// [`SUPERBLOCK_READ_LEN`] bytes (fewer when the file is shorter, which
     /// is then refused with the same end-of-file errors as a short slice).
-    pub fn parse_in(file: &dyn Storage, signature_offset: u64) -> Result<Superblock, FormatError> {
+    pub fn parse_in<S: Storage + ?Sized>(
+        file: &S,
+        signature_offset: u64,
+    ) -> Result<Superblock, FormatError> {
         if signature_offset != 0 {
             return Err(FormatError::UserBlockNotStripped(signature_offset));
         }