Ship TypeScript type declarations (.d.ts) for the public surface

[Sirivasv]

Context

bmssp is ESM JavaScript with rich JSDoc but no shipped type declarations. TypeScript consumers currently get any. Types are the single biggest DX ask for an npm library.

Scope

• Provide .d.ts for the four public exports (BMSSP, Graph, dijkstra, constantDegreeTransform) and the supported BMSSP members (calculateShortestPaths, calculateShortestPathsFrom, bmssp, reconstructPath, getEdges, and the public fields shortestPaths/nodeIDs/hops/preds).
• Options: hand-write index.d.ts, or generate from the existing JSDoc via tsc --declaration --allowJs --emitDeclarationOnly. Prefer generation if the JSDoc is complete enough, to keep types in lockstep.
• Add the types (and exports.types) field to package.json; include the .d.ts in the published files.
• Add a type-level test (e.g. tsd or a // @ts-check sample) so the types are covered in CI.

Constraints

• Types must match the locked public surface (the test/publicApi.test.mjs contract) — internal members stay untyped/@internal.
• Non-breaking (additive).

Acceptance

• A TypeScript sample importing bmssp type-checks with no any on the public surface; CI verifies it.