Compile with the new builtin syntax

The relevant changes are in these two PRs: ziglang/zig#16046 and
ziglang/zig#16163. They change the cast builtins to infer the result
type and change the order of the conversion builtins to `@xFromY`
instead of `@yToX`.

src/struct_mapping.zig

@@ -84,18 +84,18 @@ fn setValue(ctx: *Context, comptime T: type, dest: *T, value: *const Value) !voi
         .Int => {
             switch (value.*) {
                 .integer => |x| {
-                    dest.* = @intCast(@TypeOf(dest.*), x);
+                    dest.* = @intCast(x);
                 },
                 else => return error.InvalidValueType,
             }
         },
         .Float => {
             switch (value.*) {
                 .float => |x| {
-                    dest.* = @floatCast(@TypeOf(dest.*), x);
+                    dest.* = @floatCast(x);
                 },
                 .integer => |x| {
-                    dest.* = @intToFloat(@TypeOf(dest.*), x);
+                    dest.* = @floatFromInt(x);
                 },
                 else => return error.InvalidValueType,
             }