Stage 2: Edge cases + proptest invariants on core linalg/sort/distance (tracking #391)

[Mec-iS]

Tracking issue: #391 — Improve test coverage significantly (staged plan).

Scope

Edge cases and property-based invariant tests on core linalg and related primitives. Introduces proptest as a dev-dependency.

Tasks

• Add proptest to [dev-dependencies] in Cargo.toml.
• src/linalg/basic/arrays.rs (2,174 LOC, 49 existing tests but huge surface) and src/linalg/basic/matrix.rs: add #[should_panic] tests for shape mismatches and edge-case tests for empty arrays, single-element, 1×N / N×1, mismatched concat, out-of-bounds take, degenerate matmul.
• Property-based invariant tests with proptest:
  • matmul: associativity (AB)C = A(BC) where shapes allow, distributivity over addition, (AB)ᵀ = BᵀAᵀ, A·I = A.
  • transpose: involution (Aᵀ)ᵀ = A.
  • reshape: preserves total element count.
  • dot: symmetry of dot product.
• src/algorithm/sort/: property tests — quick_argsort and heap_select yield valid permutations, sorting is idempotent, sorted order holds.
• src/metrics/distance/: property tests — symmetry d(a,b) = d(b,a), triangle inequality (Minkowski/Euclidean/Manhattan), d(a,a) = 0, Hamming invariance under permutation.

Verification

• cargo test --all-features
• cargo fmt --all -- --check
• cargo clippy --all-features -- -Drust-2018-idioms -Dwarnings

Do you want to work on this issue?

yes — PR will target development.