Add ability to change mouse cursor in groups and buttons

[SamuMazzi]

Description: As described in #2248 I've implemented a way to change mouse cursor when hovering widgets. As suggested by @v-ein I've added it as a paramter to add_group, but also (for convenience IMO), I've added it to add_button.

In my Ubuntu 24 I wasn't able to render all the cursors, but I guess it's something related to the backend (actually you can set io.MouseDrawCursor to True to see all of them, but doing so degraded my performance a lot)

Closes #2248