fix: apply the superblock extension and cache image in every opener

File, MmapFile and LazyFile decoded the superblock extension and laid a
metadata cache image over the file's metadata; the other readers did
not, so the same file read differently by entry point: NativeVol,
AsyncHDF5File and MpiVol (clawhdf5-io) and the external source files of
a virtual dataset (clawhdf5-format vds.rs) read a file with an image
from its own bytes, which libhdf5 does not (they may be stale, or zeros:
h5clear_mdc_image.h5 failed with InvalidObjectHeaderVersion(0)), and
skipped the extension checks File::open makes (cve-2020-10810/10812).

Each of them owns its buffer, so each now calls the shared
superblock_ext::apply_cache_image_in_place, which checks the extension
and writes the image's entries in place (only the image block is
copied). These readers read whole datasets and cannot open a file and
fail each object, so an image libhdf5 cannot load is refused with the
image's error, never read around. clawhdf5-io's vol::load_hdf5 wraps it
for NativeVol (at open; for from_bytes the error is reported on read,
as a truncated file already was) and MpiVol. The MpiVol edit is minimal
and was not compiled: the mpi-io feature needs an MPI installation this
machine does not have (mpi-sys's build script panics).

Tests: NativeVol (open_path and from_bytes), AsyncHDF5File and a VDS
whose source file is h5clear_mdc_image.h5 (vds_interop.rs, against
h5py) read the fixture's values; the corrupted-image variants are
refused. Each fails without its fix.

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

crates/clawhdf5/tests/vds_interop.rs

@@ -486,3 +486,26 @@ fn vds_libhdf5_test_files() {
         vec![5, 10, 10]
     );
 }
+
+/// A source file with a metadata cache image (libhdf5's
+/// `h5clear_mdc_image.h5`, whose root group's header exists only in the
+/// image) is read through the image, as libhdf5 opens it. Source files were
+/// read from their own bytes, and this one failed on the root group.
+#[test]
+fn vds_source_file_with_a_metadata_cache_image() {
+    skip_if_no_python!();
+    let dir = tempfile::tempdir().unwrap();
+    let fixture = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/h5clear_mdc_image.h5");
+    std::fs::copy(&fixture, dir.path().join("src.h5")).unwrap();
+    generate(
+        dir.path(),
+        r#"
+with h5py.File("vds.h5", "w", libver="latest") as f:
+    lay = h5py.VirtualLayout(shape=(3, 100), dtype="i4")
+    lay[0:3, :] = h5py.VirtualSource("src.h5", "DSET", shape=(50, 100))[5:8, :]
+    f.create_virtual_dataset("v", lay)
+expect("vds.h5", "v", "image_source")
+"#,
+    );
+    assert_matches_libhdf5(dir.path(), "vds.h5", "v", "image_source");
+}