Record the `blosc2` feature in the changelog, the README's feature table
and the crate table, and mark the Blosc2 half of the known "Filters"
issue fixed (dated, with the conformance run that shows h5ex_d_blosc2
reading). What stays open: ZFP, writing Blosc2, and the Blosc2 features
hdf5plugin never writes (dictionaries, lazy chunks, variable-length
blocks, user-defined codecs and registered filters), which are errors.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
