Kiln in Zig - one frozen wire format, eleven from-scratch codecs

Kiln's Zig codec is one of eleven independent implementations of the Kiln serialization format, all validated against the same golden files, according to the GLD.SerializerBenchmark dashboard. The format's compactness is illustrated by the pair {"x":9,"y":-4}, which takes 14 bytes as JSON but 8 bytes in Kiln (09 00 00 00 fc ff ff ff). The Zig implementation is published on GitHub as leo-gan/gld-kiln-zig.