4.0.0: move node iteration function from Node onto DeviceTree

Also delete multiple "first" functions that can be replaced with just
calling `next` on an iterator once.

Author: leecannon

build.zig.zon

@@ -4,9 +4,9 @@
 .{
     .name = .devicetree,
 
-    .version = "3.0.1",
+    .version = "4.0.0",
 
-    .minimum_zig_version = "0.15.1",
+    .minimum_zig_version = "0.15.2",
 
     .paths = .{""},