Performance improvements for line shapes

[JCGoran]

Is your feature request related to a problem? Please describe.

The performance of the line shape could be improved, as the performance is a bit slow compared to the circular shapes.
For some performance numbers (tested with cProfile):

python -m cProfile -m data_morph --start-shape panda --target-shape star
320361688 function calls (316213771 primitive calls) in 116.715 seconds

Compare with:

python -m cProfile -m data_morph --start-shape panda --target-shape bullseye
83940221 function calls (83300500 primitive calls) in 41.067 seconds

Seems to be a factor of 4 more function calls, resulting in roughly 3x slower performance.

Describe the solution you'd like

Faster evaluation of line-line shapes.

Describe alternatives you've considered

None.

Additional context

None.

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