VRP gRPC client completeness: settings surface, e2e coverage, docs, perf nits

[ramakrishnap-nv]

Follow-up to #1597 (review nice-to-haves #5, #8, #9 + docs).

Settings surface (#9)

• The Python RoutingClient forwards only time_limit; map the rest of RoutingSolverSettings (verbose, error_logging, dump_best_results_path/interval) for parity.

E2E coverage (#5)

• The live test covers only a small cost-matrix problem; add capacity and time-window remote-vs-local cases (gated on CUOPT_GRPC_SERVER).

Perf / robustness nits (#8)

• _solution_to_py: take the solution by const ref.
• Consider bulk RepeatedField assignment and releasing the GIL in the wait loop.
• Revisit the test-driver message-size limits.

Docs

• Document cuopt.grpc.routing.RoutingClient as the GPU-less remote entry point in the package/API docs.

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