Add block name to deserialized blocks

[padix-key]

Fixes e.g. the following snippet:

import biotite.structure.io.pdbx as pdbx
import biotite.structure as struc
import biotite.database.rcsb as rcsb

pdbx_file = pdbx.CIFFile.read(rcsb.fetch("1aki", "cif", "."))
for block in pdbx_file.values():
    print(block)

[codspeed-hq]

CodSpeed Performance Report

Merging #767 will not alter performance

_{Comparing padix-key:cif-fix (0dd92e1) with main (877efed)}

Summary

✅ 59 untouched benchmarks