exact/perturb: Slight simplification
config.h: In debug mode, check if we reach OTHER_UNREACHABLE()
exact/circle_csg: Halfway towards lower degree predicates

Ray casts for depth determination now use rays at quantized y-values.
As a consequence, all circle_intersections_upwards calls share an arc
between the two compared vertices, which will allow us to reduce the
predicate degree down to six.
Merge branch 'exact' of github.com:otherlab/core into exact
exact/circle_csg: Fix indices produced by prune_small_contours

Also expose preprune_small_circle_arcs for use in the paper benchmarks.
exact/circle_predicates:

Reduce the degree of circular arc predicates from 20 to 8 (and sometimes only 6).
exact/circle_predicates: Quadrant computation is currently degree 6, not 4
exact/circle_predicates: Fix degree number in comment
exact/circle_csg: preprune_small_circle_arcs needs an IntervalScope
exact/circle_csg: Add transform operators for CircleArc
post merge with otherlab/core