Support TOML format

[134130]

Description

• I am using mise to integrate development environment setup.
• The project integrates all the asdf, cargo, npm, pip, direnv, ...
• It supports direnv, which means managements envvars, and so I migrated my projects from .env to mise.
• I am usually uses CLI, so I just change my envvars with editing my .mise.toml configuration file.
• But sometimes I uses Debug with Jetbrains Editors, that makes me need to edit my .env file or relaunch my IDE from project's root directory.

Changes

• Support TOML file format. and the [env] table's dictionaries will be loaded.
• At the first time, I tried to support mise itself, but dropped.
• If maintainer agrees or community needs, I'll make Pull request again.

Thanks!