Improve matrix handling and cbind/rbind coverage

[t-kalinowski]

Summary

• refactor r2f matrix handlers for clearer routing and TODO coverage
• add a cbind TODO handler for unsupported cases
• add cbind/rbind snapshots alongside new matrix aliasing coverage
• stabilize OpenMP parallelism behavior around matrix workloads

[codecov]

Codecov Report

❌ Patch coverage is 87.14090% with 94 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.11%. Comparing base (e8f625f) to head (e90fe2c).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
R/r2f-matrix-infer.R	74.25%	26 Missing ⚠️
R/compiler.R	69.23%	24 Missing ⚠️
R/r2f-matrix.R	89.67%	16 Missing ⚠️
R/r2f-aaa-registry.R	0.00%	9 Missing ⚠️
R/r2f.R	0.00%	8 Missing ⚠️
R/r2f-matrix-blas.R	97.44%	7 Missing ⚠️
R/quick.R	75.00%	2 Missing ⚠️
R/r2f-closures.R	95.65%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #78      +/-   ##
==========================================
- Coverage   88.70%   88.11%   -0.60%     
==========================================
  Files          17       22       +5     
  Lines        3737     3989     +252     
==========================================
+ Hits         3315     3515     +200     
- Misses        422      474      +52     

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