This removes the "Bogus distance" warnings that are otherwise generated
by `addZeroVelocityBoundary`.

The rudimentary and highly inefficicient OpenMPI "support" of the
current grid refinement implementation is not something you want to
actually use. Making this performant requires at least:

* Refinement-aware load balancing
* Load-balancing aware coupler communication (i.e. not dumbly
  communicating coupling information to processors that process
  neither the relevant coarse not the fine grid)

Until this issue is solved OpenMP delivers acceptable results on
shared-memory platforms. e.g. processing 13500 refined grid points
in `apps/adrian/cylinder2d/optimized_grid` takes about 1.3 times
as long as processing the same cell count in a uniform grid.

i.e. output cell-local quality information by default

I am not quite happy with how this looks right now but at least both
validation examples are for the most part condensed to only differ in
their refinement setup.

Perhaps a SchaeferTurek-specific "Solver" would further improve
reproducibility?

i.e. cylinder2d_optimized_grid contains roughly as many grid cells as a
uniformly resolved N=12 lattice but models the cylinder in more detail
and is more stable.

Reproducing past results for new plots is otherwise getting quite annoying.

Weirdly it seems easier to get reasonably close values for the unsteady
flow. Results for the steady flow seem to get worse when increasing
grid resolution even in uniform grids.

Finally seems to stop mixing up material numbers for every other resolution I try it out with.
Cylinder diameter is now actually set to 0.1m as called for by [SchaeferTurek96].

Makes it easier to exclude refined areas

Required to both increase cylinder discretization detail and fix cell count to a uniform N=9 grid.

This way statistics reflect the cells disabled by refinement.

Mainly to further declutter simulation and refinement setup

Somewhat fiddled together but works as expected. Refinement areas are
informed by Knudsen metric results. The key is to refine the outflow.
Sadly this requires refinement-overlap-crossing boundary conditions.

Interface for detailed (i.e. cell-relative) grid refinement control
still has room for improvement. Mixing physical indicators and cell
alignment requirements is problematic.

This allows for readable differentiation between constructor overloads.

Same result, nicer code

By deriving RefiningGrid2D from Grid2D to provide methods specific to refining subgrids.

Scaling factor is specific to the refinement method implemented by the coupler.