While this may indeed be an issue (although I have the suspicion you're the first to run into this problem), I would also take a look at how you're working with fractional floats. In particular, your match arms b'0'..=b'9' => {} and b'.' => {}, together with your implementation of Ele::val(). That is a very weird way to handle such numbers, and possibly the source of your rounding errors.

fixed.

found the issue, will fix shortly; the starting velocity should just never be 0 as shown in the description but the range of the random number generator is (incorrectly) inclusive of 0.

everything is meant to be rounded to 3 decimal places, except integers as is said in the description.