Generate one region by running the sampler over it #38

Description

Create the entrypoint that the CLI and the service call, something like generate_tile(seed, x, y). Work out the tile seed using the function from the previous ticket, build the pipeline and the region grids, hand #4 the pipeline's patch cleaning function and those grids, and return the finished grid.

Take the sampler as an argument rather than building it in here so this can be tested with a fake.

Testing:

• Assert the returned grid is one tile at full resolution
• Assert the same seed and coordinate twice give identical grids
• Assert two different coordinates give different grids
• Assert the sampler was handed the tile seed and not the global seed