Fix buffer pool race condition, pixman transform, and pixel conversion

Mark reused buffers as busy before returning from nextBuffer (before,
they only got marked busy on init).

Re-attach wl_buffer listener after re-initializing a buffer. This lets
the re-inited buffer still get a released event.

Combine scale and translate matrices with multiply instead of overwriting

Use appendAssumeCapacity for pixel conversion loop (since we already
initialized the list with the correct size).

README.md

@@ -11,6 +11,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
 These are in rough order of my priority, though no promises I do them in this order.
 
 - [ ] Switch all structs to idiomatic Zig init/deinit pattern (init returns value, caller decides stack/heap)
+- [ ] Implement runtime log levels
 - [ ] Support per-host config using properties
 - [ ] Support a basic bar
 - [ ] Support starting programs at WM launch