fix(tools): h5rs check says why the library refused a file

With the header checks merged, the library refuses truncated files and
misaligned chunk-index keys itself, so check reported only "file cannot
be opened" for a truncated file. It now reports the truncation (stored
end of file vs file length) or the library's error, and the misaligned
chunk test accepts the library's refusal of the key.

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

crates/clawhdf5-tools/src/check.rs

@@ -197,7 +197,23 @@ fn unopenable(path: &std::path::Path, out: &mut Out) -> std::io::Result<i32> {
             "no HDF5 signature at offset 0 or any power of two from 512".to_string(),
         ),
         Ok(off) => match clawhdf5_format::superblock::Superblock::parse(&data[off..], 0) {
-            Ok(_) => (off as u64, "file cannot be opened".to_string()),
+            Ok(sb) => match sb.data_end(off as u64, data.len() as u64) {
+                Err(clawhdf5_format::error::FormatError::TruncatedFile {
+                    stored_eof,
+                    actual_len,
+                }) => (
+                    0,
+                    format!(
+                        "file is truncated: the superblock's end-of-file address is \
+                         {stored_eof:#x} but the file is {actual_len:#x} bytes long"
+                    ),
+                ),
+                // Say what the library refused, not just that it did.
+                _ => match clawhdf5::File::from_bytes(data.clone()) {
+                    Err(e) => (off as u64, format!("file cannot be opened: {e}")),
+                    Ok(_) => (off as u64, "file cannot be opened".to_string()),
+                },
+            },
             Err(e) => (off as u64, format!("superblock: {e}")),
         },
     };