[FEATURE] faster (or lazy) module import

[jeertmans]

Description

Currently, Manim Slides' CLI is quite slow due to an import overhead caused by importing manim or manimlib, even though most of it is not needed.

Calling manim-slides --help takes more than 1s on my computer, when 90+ % of the time taken for importing useless modules.

However, manim-like dependencies are only ever needed when rendering slides, thus in manim_slides/slides.py.

The only attributes that are used across all tools are FFMPEG_BIN and logger, but those could be easily created apart, and eventually read options from CLI's arguments if configuration is needed (such as specifying ffmpeg's path).

A solution to this should be found, allowing for a faster CLI.

Screenshots

Snakeviz visualization when calling manim-slides --help:

Additional information

Lazy module import is only planned to be part of Python 3.12, see PEP0690, so an alternative solution should be found.