Add 39 Tier 3 ILP reductions + shared linearization helpers

[GiggleLiu]

Summary

• Adds 39 new ILP reductions for Tier 3 problems spanning graph, scheduling, flow, sequencing, matrix, and miscellaneous categories
• Adds shared ilp_helpers module with reusable linearization primitives (McCormick products, MTZ ordering, flow conservation, big-M activation, abs-diff, minimax, one-hot assignment)
• Each reduction includes closed-loop round-trip unit tests and canonical example database entries
• 81 files changed, ~10,000 lines of new code

Test plan

• make check passes (fmt + clippy + all tests)
• All 3368 tests pass (128+ new tests across 39 reductions + helpers)
• example_db coverage test verifies all registered reductions have canonical examples
• Solution pair consistency test verifies all canonical examples produce valid solutions

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 99.20976% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.84%. Comparing base (b98d3b0) to head (a40ba65).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rules/stringtostringcorrection_ilp.rs	95.18%	14 Missing ⚠️
src/rules/mixedchinesepostman_ilp.rs	97.65%	6 Missing ⚠️
src/rules/stackercrane_ilp.rs	95.71%	6 Missing ⚠️
src/rules/rootedtreestorageassignment_ilp.rs	98.29%	5 Missing ⚠️
src/rules/ruralpostman_ilp.rs	97.24%	4 Missing ⚠️
src/rules/consecutiveonessubmatrix_ilp.rs	98.30%	2 Missing ⚠️
src/rules/lengthboundeddisjointpaths_ilp.rs	98.44%	2 Missing ⚠️
src/rules/consecutiveonesmatrixaugmentation_ilp.rs	99.01%	1 Missing ⚠️
src/rules/flowshopscheduling_ilp.rs	99.24%	1 Missing ⚠️
src/rules/integralflowhomologousarcs_ilp.rs	98.27%	1 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #767      +/-   ##
==========================================
+ Coverage   97.63%   97.84%   +0.21%     
==========================================
  Files         503      583      +80     
  Lines       59714    65521    +5807     
==========================================
+ Hits        58299    64112    +5813     
+ Misses       1415     1409       -6     

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