fix(zig): make usable as a zig dependency

Make this usable as a dependency of a zig 0.12 project:

- build.zig.zon must exist to be used as a zig dependency
- public headers need to be installed as part of the artifact

build.zig

@@ -12,5 +12,7 @@ pub fn build(b: *std.Build) void {
     lib.addIncludePath(.{ .path = "lib/include" });
     lib.addIncludePath(.{ .path = "lib/src" });
 
+    lib.installHeadersDirectory(b.path("lib/include"), ".", .{});
+
     b.installArtifact(lib);
 }