Update parser for current binsparse spec and test harness

[BenBrock]

Summary

This updates binsparse-python to handle the current Binsparse 0.1 matrix descriptor shape and to work directly with the binsparse-tests harness and current
fixture files.

The old parser was limited to a narrow in-memory API and was missing several spec features used by current test data. This change brings the Python
implementation up to date for the current matrix-focused test surface.

What changed

• added spec-aware descriptor parsing and writing for:
  • version
  • number_of_stored_values
  • nested HDF5 binsparse documents
  • iso[...] value encoding
  • complex[...] value encoding
  • structure metadata
• expanded format handling to support current read paths for:
  • COO / COOR / COOC
  • CSR
  • CSC
  • DCSR
  • DCSC
• added file-based HDF5 helpers for reading and writing binsparse payloads

[BenBrock]

@ivirshup I'm planning to update the binsparse-python parser to work with the most recent version of the spec. and integrate with a new testing harness we're working on. Could you give permissions for my CI workflows to run?