Support for `justfile` and `.just` files

### Clear and concise description of the problem add support for the [just](https://github.com/casey/just) CLI ### Suggested solution `justfile` and `*.just` files should be nested ### Validations - [x] Follow our [Code of Conduct](https://github.com/antfu/.github/blob/main/CODE_OF_CONDUCT.md) - [x] Read the [Contributing Guide](https://github.com/antfu/contribute). - [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.