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/symbol_table.rs

@@ -4,7 +4,7 @@
 use alloc::vec::Vec;
 
 use crate::error::FormatError;
-use crate::storage::{Storage, len_usize, read_exact_at};
+use crate::storage::{Storage, read_exact_at};
 
 /// Symbol Table message (type 0x0011) found in v1 group object headers.
 #[derive(Debug, Clone, PartialEq)]
@@ -80,17 +80,16 @@ impl SymbolTableNode {
         offset: usize,
         offset_size: u8,
     ) -> Result<SymbolTableNode, FormatError> {
-        Self::parse_in(&file_data, offset as u64, offset_size)
+        Self::parse_in(file_data, offset as u64, offset_size)
     }
 
     /// [`Self::parse`] over any [`Storage`]: one read of the node's header,
     /// one of its entries.
-    pub fn parse_in(
-        file: &dyn Storage,
+    pub fn parse_in<S: Storage + ?Sized>(
+        file: &S,
         offset: u64,
         offset_size: u8,
     ) -> Result<SymbolTableNode, FormatError> {
-        let file_len = len_usize(file);
         // signature(4) + version(1) + reserved(1) + number_of_symbols(2) = 8
         let header = read_exact_at(file, offset, 8)?;
 
@@ -108,42 +107,22 @@ impl SymbolTableNode {
         let os = offset_size as usize;
         // Each entry: link_name_offset(os) + obj_hdr_addr(os) + cache_type(4) + reserved(4) + scratch(16)
         let entry_size = os + os + 4 + 4 + 16;
-        // `offset + 8` fits: the header's read checked it.
-        let entries_start = offset as usize + 8;
-        let needed = entries_start.checked_add(num_symbols * entry_size).ok_or(
-            FormatError::UnexpectedEof {
-                expected: usize::MAX,
-                available: file_len,
-            },
-        )?;
-        if needed > file_len {
-            return Err(FormatError::UnexpectedEof {
-                expected: needed,
-                available: file_len,
-            });
-        }
-        let body = read_exact_at(file, entries_start as u64, num_symbols * entry_size)?;
+        // `offset + 8` fits: the header's read checked it. The entries'
+        // read is the bounds check (`offset + 8 + entries > file length`,
+        // which cannot overflow: at most 65535 entries of 40 bytes).
+        let body = read_exact_at(file, offset + 8, num_symbols * entry_size)?;
         let file_data: &[u8] = &body;
 
         let mut entries = Vec::with_capacity(num_symbols);
-        let mut pos = 0usize;
-        for _ in 0..num_symbols {
-            let link_name_offset = read_offset(file_data, pos, offset_size)?;
-            pos += os;
-            let object_header_address = read_offset(file_data, pos, offset_size)?;
-            pos += os;
-            let cache_type = u32::from_le_bytes([
-                file_data[pos],
-                file_data[pos + 1],
-                file_data[pos + 2],
-                file_data[pos + 3],
-            ]);
-            pos += 4;
+        for entry in file_data.chunks_exact(entry_size) {
+            let link_name_offset = read_offset(entry, 0, offset_size)?;
+            let object_header_address = read_offset(entry, os, offset_size)?;
+            let pos = 2 * os;
+            let cache_type =
+                u32::from_le_bytes([entry[pos], entry[pos + 1], entry[pos + 2], entry[pos + 3]]);
             // reserved 4 bytes
-            pos += 4;
             let mut scratch_pad = [0u8; 16];
-            scratch_pad.copy_from_slice(&file_data[pos..pos + 16]);
-            pos += 16;
+            scratch_pad.copy_from_slice(&entry[pos + 8..pos + 24]);
 
             entries.push(SymbolTableEntry {
                 link_name_offset,