Decouple native ILP backend execution from registered pipelines

[isPANN]

Integer ILP solving currently passes through a registered integer-to-float coefficient reduction before reaching HiGHS. This refactor moves backend encoding, execution, decoding, and original-ILP validation into an internal HighsAdapter that accepts native ILP<V, C> values. Registry lookup, type-erased terminal dispatch, and source-solution extraction stay in orchestration.

All 155 registered source variants retain their ILP solving pipelines: 147 integer pipelines now stop at their original integer ILP, and eight native float pipelines retain their routes. The adapter supports all four bool/i64-variable and i64/f64-coefficient combinations, reuses the existing good_lp backend and numeric transport policy, and builds expressions without per-term temporary allocations.

The public ILPSolver::solve signature, configuration fields, error variants, and CLI/JSON/MCP result formats are preserved. Reported reduction paths now end at native ILPs. Integer coefficient transport failures use the existing InexactTransport error at the adapter boundary; assignments violating the original integer ILP use InvalidSolution instead of failing later during coefficient-cast extraction. Existing explicit coefficient-conversion reductions remain available.

Validation:

• make check passes after the final cleanup: formatting, clippy, and full workspace tests.
• make mcp-test and make paper passed during implementation.
• Regression coverage checks all four native terminals, an unregistered ILP variable domain, rounding/shape/range/constraint validation, objective overflow, and pipeline terminal invariants.
• A downstream integration test preserves generic call bounds, public struct construction, solution types, and exhaustive matching over the existing public errors.

[codecov]

Codecov Report

❌ Patch coverage is 97.21362% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.96%. Comparing base (7dd5fcd) to head (5977594).

Files with missing lines	Patch %	Lines
src/rules/ilp_i64_ilp_f64.rs	90.90%	4 Missing ⚠️
src/solvers/ilp/adapter.rs	97.43%	4 Missing ⚠️
src/unit_tests/solvers/ilp/adapter.rs	97.98%	3 Missing ⚠️
src/unit_tests/rules/ilp_i64_ilp_bool.rs	81.81%	2 Missing ⚠️
src/solvers/ilp/solver.rs	88.88%	1 Missing ⚠️
...satisfiability_directedtwocommodityintegralflow.rs	85.71%	1 Missing ⚠️
...ests/rules/ksatisfiability_preemptivescheduling.rs	75.00%	1 Missing ⚠️
...nit_tests/rules/rootedtreestorageassignment_ilp.rs	50.00%	1 Missing ⚠️
...t_tests/rules/shortestweightconstrainedpath_ilp.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1147      +/-   ##
==========================================
+ Coverage   95.93%   95.96%   +0.02%     
==========================================
  Files        1074     1076       +2     
  Lines      132106   132337     +231     
==========================================
+ Hits       126730   126991     +261     
+ Misses       5376     5346      -30     

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