Implement Kitty graphics protocol animation pause, load frame, and composite frame

[pluiedev]

Discussed in #6681

^{Originally posted by chase March 12, 2025}
Rather than implementing the full protocol (worrying about timings and such), having client controlled animation should make this much simpler to implement. Skipping blending and only allowing C=1 (no blending, just replace the destination area with the source) would be even simpler.

Animation pause would be a no-op for now, since animation isn't supported for non-controlled, but won't return an error.

Animation load frame needs to load a texture which is equal-to-or-smaller than the image it is added to, cropping the source as necessary.

Composite frame needs to take a loaded frame and the source image, compositing the loaded frame over the original texture at the provided coordinates, then display.

I'm considering taking a crack at this myself, but I know neither Zig nor the codebase, so there may be someone who is better fitted for this.

My motivation is caused by a lot of Ghostty users expecting my project to work, despite not the fact the protocol is only partially implemented: chase/awrit#62