Ability to control the "render scale" of blur effects

[logantgt]

Describe the feature

Add the ability to control the resolution at which blur effects are applied (ex. on a 3840x2160 monitor, a 0.5 "render scale" would apply the blur effect as if Hyprland were running at 1920x1080, and then use a fast/low quality scaling method to resize to the monitor resolution and paint under blurred surfaces.)

Why would it be beneficial

Ideally this would reduce the GPU load of blur effects significantly. I have a high-DPI laptop (3840x2400 at 13.4") with an Intel iGPU, and using any blur effect causes significant lag. I can run the display at a lower resolution like 1920x1200 and it performs fine, but text and UI elements become soft due to bilinear filtering (presumably used by my laptop's display hardware) scaling that framebuffer back up to 3840x2400.

There's no point in running blur passes at such a high resolution knowing the difference will be almost imperceptible, so potentially saving the performance penalty of blurring 4x the amount of pixels would be very helpful.