feat(routing): add optional distance matrix inputs to C++ models

[josembd]

Summary

This is the C++ foundation for the distance constraints and vehicle-specific
tier pricing discussed in #2018. It adds optional physical-distance matrices,
independent from the primary cost and transit-time matrices.

Changes

• Adds distance-matrix registration and accessors to the C++ data model,
  host problem storage, and CPU-to-device transfer.
• Introduces explicit cost, distance, and transit-time matrix indices.
  Matrix metadata is preserved across host/device views and fleet copies,
  while legacy cost/time layouts remain supported.
• Validates matrix dimensions, non-negative values, NaNs, and vehicle-type
  correspondence and coverage.
• Checks for an actual transit-time matrix rather than inferring its presence
  from the number of matrices.

Distance matrices remain optional. Registering one does not change route
scoring or introduce a distance constraint, tier charge, or distance-minimization
objective. API-layer exposure and distance consumers will follow in separate PRs.

Validation

12 C++ tests passed, covering registration, optional inputs, invalid values
and dimensions, vehicle-type coverage, matrix indexing, and unreachable-distance
sentinel handling.

Regression tests verify that separate distance inputs preserve the COST
objective and arrival times, and that maximum-time constraints still require
an actual transit-time matrix.

The routing and client components built successfully. Applicable pre-commit
hooks and Vale passed.

Compatibility

Existing C++ models can omit distance matrices and retain their previous
cost/time behavior.

The C++ data-model and host problem layouts gain members; native consumers
should rebuild against the updated headers and libraries.

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• docs/cuopt/source/routing-features.rst

🚧 Files skipped from review as they are similar to previous changes (1)

• docs/cuopt/source/routing-features.rst

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📝 Walkthrough

Walkthrough

The routing data model now supports optional distance matrices separately from cost and transit-time matrices. The changes add matrix registration, host/device layout handling, CPU-to-device conversion, and validation for dimensions, values, and fleet vehicle-type coverage.

Changes

Routing distance-matrix support

Layer / File(s)	Summary
Distance-matrix input and device conversion cpp/include/cuopt/routing/cpu_routing_problem.hpp, cpp/include/cuopt/routing/data_model_view.hpp, cpp/src/routing/data_model_view.cu, cpp/src/routing/cpu_routing_problem.cu, cpp/tests/routing/unit_tests/distance_matrices.cu, docs/cuopt/source/routing-features.rst	The view registers and retrieves non-owning distance matrices by vehicle type. CPU conversion checks matrix dimensions and values, copies valid matrices to device storage, and registers them with the view. Tests cover registration and CPU input validation. The documentation describes the matrix requirements and behavior.
Matrix indices and host/device layout cpp/src/routing/utilities/md_utils.hpp, cpp/src/routing/fleet_info.hpp, cpp/src/routing/vehicle_info.hpp, cpp/tests/routing/unit_tests/distance_matrices.cu	Matrix containers track cost, distance, and time indices. Matrix import packs available categories, and host and device views use the stored indices. Tests cover matrix access and CPU-to-device conversion.
Fleet coverage and solve validation cpp/src/routing/fleet_info.cu, cpp/src/routing/solver.cu, cpp/tests/routing/CMakeLists.txt, cpp/tests/routing/unit_tests/distance_matrices.cu	Fleet setup checks distance-matrix coverage and values. Solver validation checks maximum-time constraints against transit-time matrix availability. Tests cover these checks, device input validation, and models without distance matrices.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Suggested reviewers: afender

Merge Risk: ⚪ Minimal · up to 2f369

The previously short heading underline is fixed. No actionable issue remains in the selected documentation change.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 1.92% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 52 functions across 10 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding optional distance matrix inputs to C++ routing models.
Description check	✅ Passed	The description is directly related to the changeset. It covers distance-matrix support, matrix indexing, validation, compatibility, testing, and build results.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 1.92% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 52 functions across 10 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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Inline comments:
Review comments at @docs/cuopt/source/routing-features.rst:
- Around line 132-133: Extend the underline beneath the “Independent Distance
Matrices” heading by one character so it matches the title length and avoids a
Sphinx warning.

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📥 Commits

Reviewing files that changed from the base of the PR and between a42e4ca and 8177d06.

📒 Files selected for processing (12)

• cpp/include/cuopt/routing/cpu_routing_problem.hpp
• cpp/include/cuopt/routing/data_model_view.hpp
• cpp/src/routing/cpu_routing_problem.cu
• cpp/src/routing/data_model_view.cu
• cpp/src/routing/fleet_info.cu
• cpp/src/routing/fleet_info.hpp
• cpp/src/routing/solver.cu
• cpp/src/routing/utilities/md_utils.hpp
• cpp/src/routing/vehicle_info.hpp
• cpp/tests/routing/CMakeLists.txt
• cpp/tests/routing/unit_tests/distance_matrices.cu
• docs/cuopt/source/routing-features.rst

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