ci: build the Python package with maturin and run its tests against h5py

ci-test.sh gains a step that lints clawhdf5-py, builds its wheel with
maturin, unpacks it under target/ (the interpreter's environment is not
touched) and runs the pytest suite, which compares reads with h5py. It
skips without maturin/pytest, and fails instead under
CLAWHDF5_REQUIRE_INTEROP=1. The CI interop venv installs maturin and
pytest, so CI runs it.

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

CHANGELOG.md

@@ -41,6 +41,11 @@
   h5py 3.16 (HDF5 2.0) on a file h5py writes. One difference is h5py's:
   it returns variable-length sequences of big-endian floats unswapped; this
   package returns the stored values.
+- **CI builds and tests the Python package.** It was excluded from CI.
+  `scripts/ci-test.sh` now lints `clawhdf5-py`, builds the wheel with
+  maturin, unpacks it under `target/` and runs the pytest suite; skipped
+  without maturin/pytest in `$CLAWHDF5_PYTHON`, a failure then under
+  `CLAWHDF5_REQUIRE_INTEROP=1`. The CI interop venv installs both.
 
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