routing: unify snapping/routing semantics across single-route and batch APIs

[blackopsrepl]

Summary

• make compute_matrix use the same node-snapped routing model as the existing public single-route APIs
• keep the explicit edge-snapped path APIs available separately instead of mixing semantics implicitly
• add a deterministic regression test proving matrix times match route(...) on the same input pair

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test matrix::matrix_matches_single_route_node_snapping --test integration
• cargo test (blocked by a pre-existing routing::osrm_comparison::duration_matches_osrm failure also present on main)

Fixes #2