Improve MATLAB bindings (SSMC pipeline, type minimization, allocator safety, tests)

[BenBrock]

Overview

• Added end‑to‑end SSMC pipeline in MATLAB, expanded SSMC conversion to support dense inputs, and
  introduced comprehensive tests.
• Improved type minimization (float→int, ISO pass) and allocator correctness for MATLAB MEX bindings.
• Fixed empty‑array handling to avoid uninitialized reads and invalid class IDs.

Key changes

• binsparse_from_ssmc
  • Supports dense vectors/matrices (DVEC/DMAT) and optional Zeros.
  • Default format is COO; dense inputs enforce DVEC/DMAT.
  • Uses allocator‑aware bsp_convert_matrix_allocator.
• New MATLAB function generate_bsp_from_ssmc
  • Converts primary matrix and aux/x/b, minimizes types, writes to HDF5 root/aux groups.
  • Defaults: format='COO', compression_level=0.
• New tests
  • test_generate_bsp_from_ssmc
  • test_binsparse_from_ssmc
  • test_binsparse_minimize_roundtrip
• Type minimization upgrades
  • Downcast float→int when all values are integral.
  • ISO pass to compress equal‑valued arrays; special‑case iso[bint8] for value=1.
• Allocator consistency and safety
  • Added bsp_convert_matrix_allocator and restored bsp_convert_matrix wrapper.
  • Removed mexMakeMemoryPersistent allocator in binsparse_read.c.
  • Fixed empty array conversions (now 0×1 with valid type fallback).
  • MATLAB helpers are header‑only; build scripts updated accordingly.

Files touched (high level)

• bindings/matlab/
  • New: generate_bsp_from_ssmc.m, test_generate_bsp_from_ssmc.m
  • Updated: binsparse_from_ssmc.c, binsparse_minimize_types.c, binsparse_read.c,
    Contents.m, build scripts
  • Helpers now header‑only in matlab_bsp_helpers.h
• include/binsparse/convert_matrix.h
  • Added allocator‑aware conversion API.

Notes

• Metadata handling is intentionally deferred; string aux entries are currently ignored with a note.
• HDF5 dataset ordering is not guaranteed unless link order is enabled in library code (unchanged).

Testing

• build_matlab_bindings
• test_generate_bsp_from_ssmc
• test_binsparse_from_ssmc
• test_binsparse_minimize_roundtrip