`intersect!` should handle colliding path decorations

Right now, `intersect!` replaces a segment of the crossing-over path with a crossover according to the supplied crossover style. This removes any decorations on that segment, but we might also want to remove bridges within a certain margin of the crossover that might have been placed beforehand. It also doesn't touch the crossed-over path, which, for example, could coincidentally have its own bridge near the crossover point. It should remove decorations within some specified margin on both paths by default (with an option to turn that off).

(More generally, it might be useful to have a related method use spatial indexing to detect intersecting decorations and remove one in any collision.)

Start by locating the Julia implementation of intersect! and inspect how crossover styles replace path segments and how bridges or other decorations are represented. Define the margin and opt-out behavior for both paths, then verify that nearby decorations are removed without affecting unrelated geometry; the broader spatial-indexing idea is separate scope.

Written by the indexing model from the issue text.