Load settings from .toml files, .env and environment variables. Also ensures a ROOT_PATH environment variable is
set. If ROOT_PATH is not set and no root_path argument is passed, the current working directory is used as root.
Settings paths can be a single .toml file, a folder containing .toml files or a list of .toml files and folders.
If a folder is passed, all .toml files in the folder are loaded. If settings path is None, only .env and
environment variables are loaded. If settings_path are relative paths, they are joined with the root_path argument.
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