Add triangular lattice topology and subset generation

[Ferrari-72]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 80.95238% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/graphio/udg.jl	80.95%	16 Missing ⚠️

Files with missing lines	Coverage Δ
src/graphio/udg.jl	57.83% <80.95%> (+20.80%)	⬆️

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[Ferrari-72]

What changed

1. Move strategy decisions to the top level
   • Dedup strategy selection is now centralized in generate_triangular_udg_subsets (entry point).
   • dedup_inner_subsets now focuses on executing the selected strategy, instead of making implicit fallback decisions.
2. Fail fast instead of silent fallback
   • dedup_inner_subsets(...; use_shortg=true) now throws ArgumentError if shortg is unavailable.
   • Added strict_dedup; in strict mode, unmet prerequisites fail immediately.
3. Explicit fallback behavior
   • At the entry point, if shortg is unavailable, we explicitly fall back to g6-string dedup with a warning.
   • This prevents “deduplication appears enabled but is effectively skipped” behavior.

Test improvements

• Added tests for strict_dedup argument constraints.
• Added tests for the use_shortg=true + missing shortg failure path.
• Added behavior tests comparing raw vs deduplicated outputs (count + structure assertions).

Validation

• julia --project test/graphio/udg.jl passes.