refactor: teach both adapters to draw any ring

The chart tiled rectangles and the globe draped quads, which was the
last place the grid assumed its cells were rectangles of the picture.
Both adapters now take the system's ring as it comes: the chart draws
a plain polygon while the loop stays on the sheet, closes a pole
cell's loop along the pole's own edge, and splits a ring that stayed
continuous across the antimeridian into its two visible pieces with a
small pure clipper; the globe drapes the ring directly -- unwrapped
longitudes just carry past 180, because the trigonometry underneath is
periodic -- and fills it as a fan from the cell's own centre, spokes
densified by span so the sheet follows the curve instead of opening
into almond-shaped gaps between them.

For geohash nothing observable moves: the parity tour reads identical
across all thirty-two steps, and the clipper is exercised only by its
unit tests until a system with real geodesic cells arrives.

commit

56800ad9766c00d03313103e32be1b3e737b20af

parent

d79bab2d3806183316fcddad04754a6ee016e5b9

author

Dami <dami.etoile@gmail.com>