Add route-level generic Request/Response typing to TypeScript definitions

[Copilot]

The current TypeScript declarations do not allow route handlers to express narrowed request shapes or enforce response body contracts. This change introduces non-breaking generics across the handler/middleware/route type surface so routes can opt into strongly typed input/output.

• Type surface: generic request/response plumbing

  • Middleware, ErrorHandlingMiddleware, and HandlerFunction now accept <TRequest, TResponse> generics (defaulting to existing Request/Response behavior).
  • API route registration methods (get, post, put, patch, delete, options, head, any, METHOD) and use overloads now carry those generics to route-level declarations.

• Response body contract typing

  • Response is now generic: Response<TBody = any>.
  • send, json, and jsonp are typed to TBody, enabling compile-time enforcement of response payload shape.

• Type tests (tsd) for generic behavior

  • Added tests for:
    • extended Request usage in typed handlers,
    • typed Response<TBody> payload enforcement,
    • route registration with explicit generic request/response types,
    • rejection of invalid response payload shapes.

interface TypedRequest extends Request {
  params: { thingId: string; anotherThingId: string };
}

interface TypedResponseBody {
  hello: string;
  foo: string;
}

api.get<TypedRequest, Response<TypedResponseBody>>('/typed', (req, res) => {
  res.json({
    hello: req.params.thingId,
    foo: req.params.anotherThingId,
  });
});