WIP: Refactor config and related stuff

[Viicos]

Fixes #3466.

What technically changed:

• Use pydantic to create a new ManimConfig class, providing built-in type hints, validation. This eliminates the need to define properties for each parameter.
• Remove the need to have a default.cfg file where defaults were stored. Instead, default values are set on the ManimConfig class directly (making it easier to keep in sync).
• Fortunately, most of the existing config options were standard types (meaning supported out of the box by Pydantic). ManimColor was the only exception, so a custom annotation was created (see docs for more details; TLDR the ManimColor class in untouched and not tied to Pydantic in any way, the custom annotation simply provides info about how to validate/parse input, and how JSON schema should be generated).

What functionally changed:

• Decouple the config model from file parsing. To do so, an abstract ConfigProvider class was added, exposing a get_config method. Each subclass of ConfigProvider is responsible for parsing a specific config format (for now, only CfgProvider is implemented and provides an instance of ManimConfig parsed from .cfg files).
• In the future, users will be able to use other file formats such as TOML (the new standard in Python). Unlike cfg, TOML is well-specified and easier to parse because of the built-in types it supports. Thanks to the use of Pydantic, a JSON schema can be generated and used in IDEs to provide autocomplete when writing configuration files.
• The structure of the ManimConfig class has slightly changed. Mainly:

Before	After
ffmeg_loglevel	ffmpeg.loglevel
ffmpeg_executable	ffmpeg.executable
verbosity	logging.verbosity
media_embed	jupyter.media_embed
media_width	jupyter.media_width

properties with deprecation warnings where added to avoid any breaking changes.

• the CLI_CTX section is now made available in the config, through the cli_formatting attribute. cloup context settings are made accessible through the cli_formatting.context_settings property.

TODO

• Implement tex_template / tex_template_file
• Implement custom_folders. Needs investigation, confusing? Still required?
• Set default values to input_file / output_file (only set through the CLI)
• Implement get_dir
• Implement ManimFrame
• Parse CLI args (that is re-implement digest_args)
• Implement support for tex_template/tex_template_file: Might need some refactor to the related tex classes.
• Choose a serialization format for ManimColor
• Docstrings
• Extensive testing
• Rename CLI switch to CLI flag in docstrings?

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

[MrDiver]

Looking forward to this change!

[JasonGrace2282]

Heyo, are there any updates as to how the progress here is going? I'm interested in helping out here :)