FR: Add optimized cached blur

Hyprland version
PASTE YOUR HYPRLAND VERSION HERE (hyprctl version), BETWEEN THE BACKTICKS. DO NOT REMOVE ANY FORMATTING.

I wanted to request this feature which would massively help the non discrete gpu pcs with integrated graphics be able to run blur effects.

My feature request is to have a variable or mode called cached blur where if enabled, what it does is it everytime bg changes generates a blurred image based on blur settings and then stores it in the memory.

Now we want to apply the blur, so instead of the current way of applying everyframe post processing effects, the saved burred cached image from the memory can be used and passed as bg for the window while the global bg stays unaffected.

This way we can save a lot of compute and the low end pcs too will be able to afford blur.

This was my idea.
Thanks.

this is already done and has been for 4 years