Fix Procedural SVG Generation Bugs in Javascript

Seeking a strong-ish background either with SVG curve types, or at least the mathematics behind them.

I have noted (in this archive: https://drive.google.com/file/d/1dxV0Q5YQPrKkNFXWi6h4Q0Ca6zvWiU-y/view?usp=sharing) the specific issues that need fixing, both in the code (in the comments marked 'FIXME'), and also in the accompanying screenshot showing both an example of non-overlap (expected behaviour, marked in green) and overlap (wrong behaviour, marked in red).

However the nodes are positioned relative to each-other (they can be moved by drag-and-drop around the canvas), the edge geometry (whenever there are two *or more* edges) between them must remain clearly separated and non-overlapping. The solution must also not break the single-edge case. Ideally, there will be smooth transitions as the curves change upon repositioning nodes, but it's more important that - when stationary - that the curves don't overlap.

The main relevant areas of the code for this task are circleRectDelta(), circleCircleDelta(), and the _mutualTotal > 1 case in Edge.resetGeometry(). SVG geometry types, in case you're unfamiliar, are documented here: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/d