[sjdoane]

An HDF checkpoint can store the RNG algorithm name as fixed-width bytes (b'MT19937'). HDFBackend.random_state returns those bytes unchanged, and NumPy rejects the state when EnsembleSampler reopens the checkpoint. This addresses the fixed-byte-name failure described in #331.

Decode the first RNG-state element when it is bytes. Text identifiers and the remaining state, including the Gaussian cache, stay unchanged. Reading does not modify the checkpoint or introduce a new storage schema.

Validation:

• Added cases against original source: 4 failures / 2 text controls pass. Entire existing/new unit collection: 4 failures / 102 passes before; 106 passes after.
• The 106 unit tests pass on Python 3.9 / NumPy 2.0 / h5py 3.14 and Python 3.12 / NumPy 2.5 / h5py 3.16, macOS arm64. All configured pre-commit hooks pass.
• A separate checkout independently repeats the baseline and patched unit tests. Actual HDF byte/text attributes, custom groups, read-only file nonmutation, restored RNG output and exact short checkpoint continuation are checked.

The fixtures use current h5py to reproduce fixed-width byte storage; an original Python 2-created file and general Python 2 compatibility were not tested. Full integration tests, other platforms and hosted CI remain unverified.

Implementation and independent local review were performed by separate Codex agents.