feat: add concrete application engines and bounded multidimensional indexes

[josephjohncox]

Summary

• adds 50 concrete, reusable application engines across partitioning, scheduling, catalogs, allocation, and leasing, each with an executable example, independent oracle, focused tests, benchmark, and scenario documentation
• adds experimental identity-preserving multidimensional indexes: the linear BoxIndex, fixed BoxIndex2D/3D/4D axis-projection indexes, and guarded BoundedBoxIndex
• hardens RangeSet payload ownership, callback reentrancy, failure atomicity, and compatibility with the original three-method structural PayloadPolicy contract
• adds correctness-attested application and bounded-box benchmarks, immutable diagnostics, resource/memory guardrails, packaging checks, and monorepo-authoritative docs/examples
• preserves RangeSet as the stable one-dimensional API; multidimensional types remain experimental namespace-only exports

Validation

• just validate: 977 passed, 18 skipped; stable backends 30 passed
• just check: 955 passed, 15 skipped, 25 deselected; 95.24% branch coverage
• just run-examples: all 54 examples passed from /tmp
• application benchmarks: all 50 scenarios validated in smoke (1 × 8 operations) and standard (5 × 64 operations) profiles
• core benchmark smoke and standard profiles passed across all six stable backends
• bounded-box benchmark: five timed instances matched the independent oracle and final state; no universal ranking claim
• clean git archive wheel/sdist build, artifact-policy verification, and arbitrary-CWD clean-wheel install passed
• independent final integration review: ACCEPT, no blockers

Platform notes

Validated locally on macOS arm64 with Python 3.12. CUDA, Metal-device, Boost ICL, and the full cross-platform release matrix remain CI/hardware-lane responsibilities. Experimental accelerators are not automatically selectable stable backends.