feat: split sheets that hold several places into their own maps or layers

Two maps are published as one tile sheet carrying more than one place. Tears
of the Kingdom stacks three elevations of Hyrule down a single sheet, so two
thirds of it is scrolled past to reach the Depths. The Mojave Wasteland rings
its main map with eight district insets, which sit in the margins as boxes
with no way to reach them.

The split is already in the data: the top-level regions are the pieces, and
every location names one. A sheet is taken apart into its pieces, offered
either as separate maps or as layers of one map. Separate maps suit places
that merely share a sheet, and reset the view. Layers suit the same ground at
different heights, and carry the view across by its position within each
layer's box, so switching from Surface to Depths leaves the reader over the
same part of Hyrule.

Which maps to split is declared, not detected. Breath of the Wild has fifteen
top-level regions and Palworld forty-two, and those are areas of one map:
splitting them would shatter it. Nothing in the data separates Mojave's nine
leaf regions from Hyrule's fifteen.

A piece is sized by the ground its regions cover, not by the locations
assigned to it. Sizing it to reach every location pulled the Mojave map back
over the very insets it was being split from, because forty of its locations
sit outside the region that claims them. Those are reported during generation
and stay reachable, since bounds clip the raster and not the pins.

commit

2ae277511a3b6b25b4dd948fe73153e569fe16eb

parent

0a352a3eb571c10b2450cfe3d6fbea6470c6b6a3

author

Dami <dami.etoile@gmail.com>