Feature request: invert_position option + percentage support for covers

[iouribecq]

Hello,

First of all, thanks a lot for the AirSend integration, it works great!

I have two requests regarding covers (stores / shade sails):

1. Invert position option
   For devices like shade sails or projector screens, the open/close logic is reversed compared to standard roller shutters.
   Example:

   • Sail up = closed
   • Sail down = open
     An option like invert_position: true would solve this easily (similar to invert_open_close in mqtt.cover).

2. Percentage support (if possible)
   Some AirSend devices support a "pseudo position feedback" based on the duration of opening/closing.
   Would it be possible to expose this as a current_position attribute in Home Assistant, so the user could use a percentage slider?
   This would allow more precise control (e.g. 30 % shade).

If AirSend hardware does not expose any state feedback, I totally understand, but if the API already provides timing-based estimation, it would be great to have it in Home Assistant.

Thanks a lot