cloup.Group ignores command class to produce sub-commands

cloup.Group ignores command class to produce sub-commands: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). cloup.Group ignore the command class property (https://github.com/pallets/click/blob/d9af5cfa009c927a96d10ed38a3e37979876a12e/src/click/core.py L1797-L1802)…

The task

`cloup.Group` ignore the [`command_class` property](https://github.com/pallets/click/blob/d9af5cfa009c927a96d10ed38a3e37979876a12e/src/click/core.py#L1797-L1802) that is [used in `click.Group` to set the default class of the `@group.command()`…

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.