Add DirectLoader mode to default Cucumber test suite

[mjjbell]

Feature

Currently npm test runs the Cucumber suite with a matrix configuration for selecting the algorithm (CH, MLD) and data loading (shared-memory, mmap) options.

However, there is a third data loading option, 'direct load', which is to directly load the datasets into the osrm-routed process memory.

The code paths for each data loading option are distinct

• Storage::Run + SharedMemoryAllocator
• MMapMemoryAllocator
• ProcessMemoryAllocator

It would be wise to include direct data loading as part of the Cucumber configuration matrix, even more so given I plan to make changes to support optional datasets.

To keep runtime down in CI, we could run direct loading on only a handful of jobs, or split the CI flow to run Cucumber tests as a parallel substep for each build configuration.

This will also help tidy up the handful of direct load tests that erroneously run in shared memory and mmap mode.