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/chunked_write.rs

@@ -2125,7 +2125,7 @@ mod tests {
             for info in &infos {
                 // Skipped chunks are stored at the chunk's size (shuffled).
                 assert_eq!(
-                    info.chunk_size == (c * 8) as u32,
+                    info.chunk_size == (c * 8) as u64,
                     info.filter_mask != 0,
                     "{info:?}"
                 );