fix busyloop while waiting for WlBuffers to be released

[LGFae]

We changed from SlotPool to Multipool, which let us fix the busyloop. Suggested by @YaLTeR.

Fixes #202.

[LGFae]

Just finished testing with niri. It appears to be working.

[YaLTeR]

Just gave it a try, while it seems to work, the damage tracking or something appears to be broken? There are some buffer glitches.

[YaLTeR]

out.mp4

[LGFae]

Jesus Christ. I wonder why that didn't show up over here? I tested it inside River, maybe I should have spawned a new tty. I'll do that now.

[LGFae]

Hmm. I am actually incapable of reproducing that. I thought this would damage the entire surface:

        let surface = self.layer_surface.wl_surface();
        surface.attach(Some(buf), 0, 0);
        surface.damage_buffer(0, 0, width, height);
        surface.commit();

So, because we damage the entire surface every time, I don't think it's the damage tracking...

[YaLTeR]

Yeah, weird.. Maybe something to do with buffer format?

[LGFae]

The buffer format didn't change. It remains Xrgb8888, which is guaranteed to exist by the protocol.