feat: lake: alternative TOML config

[tydeu]

Work-in-progress PR for an alternative TOML configuration file for basic packages.

Task list

• [x] TOML parser
• [x] TOML data types
• [x] TOML elaborator (Syntax -> data types)
• [x] TOML tests
• [ ] Lake configuration from TOML
• [x] lakefile.toml loader
• [ ] lake translate <toml|lean> to switch between config languages
• [ ] TOML option for Lake package templates (e.g., lake init <pkg> --toml)