ci: lint all targets, run interop suites for real, compile benches

- clippy --all-targets plus a clawhdf5-format feature matrix (parallel, lz4,
  zstd, pcodec, fast-checksum); fix the accumulated lint backlog in test,
  bench and feature-gated code (no behaviour changes).
- Install python3 + h5py/numpy/netCDF4/xarray in the CI container and set
  CLAWHDF5_REQUIRE_INTEROP=1, which makes a missing interop dependency a test
  failure. Every h5py/netCDF4 interop test used to skip silently in CI. Run
  the #[ignore]d writer_h5py_tests suite explicitly.
- cargo bench --no-run so benches can't rot; fix bench.rs and memory_bench.rs,
  which no longer compiled against the current strategy/consolidation APIs.
- Optional fuzz smoke run via CLAWHDF5_FUZZ_SECONDS.
- CHANGELOG and docs/known-issues.md updated.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/known-issues.md

@@ -72,11 +72,38 @@ generated yet; one written with the C API (`H5T_STD_REF`) is needed.
 
 ## `clawhdf5-gpu` `gpu_tests` can hang under the default parallel test runner
 
-**Status:** open. Observed 2026-09-18 (RTX 5060 Ti, Linux).
+**Status:** fixed 2026-09-19.
 
-**Summary:** during `cargo test --workspace`, the `gpu_tests` binary sat idle
-(~1% CPU) for 25+ minutes and had to be killed. Run single-threaded it passes
-in seconds (20/20): `cargo test -p clawhdf5-gpu --test gpu_tests -- --test-threads=1`.
-Suspected cause: several tests creating wgpu devices concurrently (possibly
-compounded by the rest of the workspace's tests loading the machine). Not yet
-root-caused; workaround is `--test-threads=1` for that crate.
+**Summary:** during `cargo test --workspace` the `gpu_tests` binary sat idle for
+25+ minutes. Every test created its own `wgpu::Instance` + device (requesting
+adapter-maximum limits) concurrently, and readback used an unbounded
+`device.poll(Wait)`.
+
+**Fix:** tests hold a process-wide lock while they own a device, and
+`GpuAccelerator` readback waits time out after 30 s with `GpuError::BufferMap`.
+
+## Compound datatype versions 1 and 2 are mis-parsed (default libver files)
+
+**Status:** fixed 2026-09-19. Found by adding a default-libver axis to the h5py
+interop tests.
+
+**Summary:** any compound dataset written with default libver bounds (plain
+`h5py.File(path, 'w')`, datatype message version 1) failed to read, typically
+with `Overflow("compound member 'x': byte_offset(0) + field_size(4136977) ...")`.
+Only `libver='latest'` files (version 3+) and files written by clawhdf5 itself
+worked, which is why the existing tests never caught it.
+
+**Root cause:** `Datatype::parse` skipped 24 bytes of legacy per-member array
+fields for v1 where the format has 28 (dimensionality 1 + reserved 3 +
+permutation 4 + reserved 4 + 4 dimension sizes 16), and treated v2 like v1 minus
+name padding, whereas v2 keeps the 8-byte name padding and has no array fields.
+
+## Attributes with unsupported datatypes are silently dropped
+
+**Status:** open.
+
+**Summary:** `Dataset::attrs()` / `Group::attrs()` in the `clawhdf5` facade return
+only attributes convertible to `AttrValue`. An attribute with, e.g., a compound
+datatype is omitted from the map with no error or indication that it exists.
+Planned: surface these as an explicit `AttrValue` variant (raw bytes + datatype)
+or an error, as part of the "no silent skips" robustness work.