Add lazy EMD solver with O(n) memory requirement

[nathanneike]

Add lazy EMD solver with on-the-fly distance computation

• Implement emd_c_lazy in C++ network simplex for memory-efficient OT
• Add lazy mode to emd2() accepting coordinates (X_a, X_b) instead of cost matrix
• Support sqeuclidean, euclidean, and cityblock metrics
• Add restrict for SIMD optimization
• Remove debug output from network_simplex_simple.h
• Add tests for lazy solver and metric variants

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Motivation and context / Related issue

Addresses memory limitations when computing OT with large point clouds. Instead of pre-computing and storing the full n×m cost matrix, the lazy solver computes distances on-the-fly during the network simplex algorithm. This reduces memory from O(nm) to O(n+m) while maintaining exact EMD solutions.

How has this been tested

• All existing tests pass (1031 passed, 69 skipped)
• Added new tests in test_solvers.py: test_solve_sample_lazy and test_solve_sample_lazy_emd
• Verified correctness against standard EMD solver
• Tested all three metrics (sqeuclidean, euclidean, cityblock)
• Confirmed SIMD optimization with compiler output analysis

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[rflamary]

use @pytest.mark.parametrize to check teh metrics instead of a loop inside test

[rflamary]

This is too much of an API change please create a new function emd2_lazy

[codecov]

Codecov Report

❌ Patch coverage is 93.04348% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.03%. Comparing base (4c49769) to head (cd61070).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #788      +/-   ##
==========================================
- Coverage   97.07%   97.03%   -0.04%     
==========================================
  Files         107      107              
  Lines       22156    22249      +93     
==========================================
+ Hits        21507    21590      +83     
- Misses        649      659      +10     

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