Read chunks of 4 GiB or more in every chunk index

ChunkInfo::chunk_size (and ChunkMapping::file_size) are u64: sizes past
u32 were truncated for Single Chunk, Implicit, Fixed and Extensible Array
indexes, and a v2 B-tree index refused them. A selection of a chunked
dataset with a non-default fill value is read over a box of fill values
instead of a full read, an unfiltered chunk of a file that is not in memory
is read row by row, and an intermediate deflate stage no longer reserves the
chunk's whole bound.

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

crates/clawhdf5-format/src/fixed_array.rs

@@ -383,7 +383,7 @@ fn parse_fa_element(
     offset_size: u8,
     element_size: u8,
     chunk_byte_size: u64,
-) -> Result<Option<(u64, u32, u32)>, FormatError> {
+) -> Result<Option<(u64, u64, u32)>, FormatError> {
     let os = offset_size as usize;
     if client_id == 0 {
         // Non-filtered: element is just the chunk address.
@@ -393,7 +393,7 @@ fn parse_fa_element(
             return Ok(None);
         }
         let address = read_offset(file_data, abs, offset_size)?;
-        Ok(Some((address, chunk_byte_size as u32, 0)))
+        Ok(Some((address, chunk_byte_size, 0)))
     } else {
         // Filtered: address(offset_size) + chunk_size(variable) + filter_mask(4)
         let es = element_size as usize;
@@ -418,7 +418,7 @@ fn parse_fa_element(
             file_data[fm_off + 2],
             file_data[fm_off + 3],
         ]);
-        Ok(Some((address, chunk_size as u32, filter_mask)))
+        Ok(Some((address, chunk_size, filter_mask)))
     }
 }
 
@@ -688,7 +688,7 @@ mod tests {
             assert_eq!(c.address, base_addr + i as u64 * chunk_byte_size as u64);
             assert_eq!(c.offsets, vec![i as u64 * 20]);
             assert_eq!(c.filter_mask, 0);
-            assert_eq!(c.chunk_size, chunk_byte_size as u32);
+            assert_eq!(c.chunk_size, chunk_byte_size as u64);
         }
     }