Optimize always_redraw() by reducing Mobject copying in Mobject.become()

[chopan050]

Overview: What does this pull request change?

Inside the method Mobject.become(self, mobject, ...) where self morphs into a target mobject, the latter was always copied before the morphing. Now, it's copied only when it's explicitly altered (when stretch or match_[height|width|depth|center] is True), which is rarely the case. This optimizes Mobject.become() in most cases and, therefore, leads to a speedup when using always_redraw(), which under the hood creates a Mobject with a become() updater attached to it.

Motivation and Explanation: Why and how do your changes improve the library?

Copying Mobjects is expensive, so it should be done only when necessary. In the case of Mobject.become(), one usually calls it without specifying stretch or match_[height|width|depth|center] which are all False by default. In that case, the target mobject is not modified at all, so it's not necessary to copy it before making self morph into it.

By removing the copy in that case, Mobject.become() gets a lot faster. By profiling the following code:

if __name__ == "__main__":
    with tempconfig({"quality": "low_quality"}):
        SineCurveUnitCircle().render()

where SineCurveUnitCircle is a scene from the example gallery, I get the following results showing around 4x speedup in Mobject.become():

Before	After

Links to added or changed documentation pages

Further Information and Comments

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