Created and optimized Bézier splitting functions such as partial_bezier_points() in manim.utils.bezier

[chopan050]

Overview: What does this pull request change?

Related PR: #3281

The original algorithm in partial_bezier_points() made a lot of calls to bezier(), making multiple redundant intermediate calculations that could've been reused for the other Béziers.

Instead, in the n-th degree case I calculate all of the necessary points in a single pass, improving from O(n³) to O(n²) time:

def partial_bezier_points(points, a, b):
    # Border cases...
    
    degree = points.shape[0] - 1
    if degree == 3:
        # calculate portion_matrix..
        return portion_matrix @ points
    # if degree in (2, 1, 0)...

    # Fallback case for nth degree Béziers
    # It is convenient that np.array copies points
    arr = np.array(points)
    N = arr.shape[0]
    
    if a != 0:
        for i in range(1, N):
            arr[: N - i] += a * (arr[1 : N - i + 1] - arr[: N - i])

    if b != 1:
        if a != 0:
            mu = (1 - b) / (1 - a)
        else:
            mu = 1 - b
        for i in range(1, N):
            arr[i:] += mu * (arr[i - 1 : -1] - arr[i:])

    return arr

Even more, the process can be encoded as a matrix multiplication, which is what I did for the simple cases (up to cubic curves), giving around 10x speedup:

    if degree == 2:
        ma, mb = 1 - a, 1 - b

        portion_matrix = np.array(
            [
                [ma * ma, 2 * a * ma, a * a],
                [ma * mb, a * mb + ma * b, a * b],
                [mb * mb, 2 * b * mb, b * b],
            ]
        )
        return portion_matrix @ points

This rewritten function can now replace partial_quadratic_bezier_points().

I applied the exact same process for creating split_bezier() and subdivide_bezier(), which are very similar and use essentially the same algorithm, and can also be encoded as matrix multiplications. Moreover, subdivide_bezier() creates memos for each generated matrix, to reuse them in future calls to the function. Currently split_bezier() isn't being used anywhere (originally subdivide_quadratic_bezier() used split_quadratic_bezier()), but I still leave it there because its docstring is useful and it might be used in the future for something else.

I also created bezier_remap(), based on quadratic_bezier_remap(), which uses subdivide_bezier(). I noticed that VMobject.insert_n_curves_to_point_list() uses an algorithm that could've been a call to bezier_remap(), so I used that instead.

All of this is thoroughly documented in docstrings, being the most important one the split_bezier() docstring, where the algorithm is explained in depth. The other docstrings are based on this explanation.

I also added many tests for many different cases.

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[JasonGrace2282]

LGTM, thanks!