Tweak many gizmos stress test

[vby]

Objective

Make the stress test example many_gizmos a little bit more fun.

Solution

Draw random lines in a cube, seeding by the elapsed seconds.

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[james7132]

The variability introduced by this make it difficult to use this as a stress test. Not sure if we should do this.

[nicopap]

This was discussed in the gizmos PR. #6529 (comment)

I agree with james in that it makes it difficult to use it as a benchmark.

Maybe instead of replacing the "simple" setup, you could add more setups? Replacing Config.fancy: bool by an enum that cycles between "simple black line" "disc", "cube" etc.

[vby]

Remove variability if fancy is off, the state is constant now.