This is considerably more efficient to read and to update compared to the
manually maintained o5m pyramid used so far, at the cost of a lot of disk
space.

The OSMX usage is extremely primitive so far, relying solely on its command
line tool. We could gain a bit more performance still by using OSMX API
directly and avoiding the PBF file indirection, but that is in the ~1%
range, and technically not entirely straightforward due to how OSMX is
built and its bundled dependencies.

This code will be used by the upcoming Tirex backend for on-demand tile
generation, existing code is only touched for removing a small bit of
dead code.