refactor: move meta and random modules from vm and cli into new aux library category

Restructure module hierarchy by extracting meta and random from the core VM and CLI-specific modules into a new "aux" (auxiliary) directory. This introduces WREN_AUX_META and WREN_AUX_RANDOM configuration flags, updates include paths and build system to compile aux sources separately, removes random module registration from CLI modules.c, and adjusts the VM's module loading to implicitly import core into all modules regardless of name.

builtin/meta.wren

@@ -1,13 +0,0 @@
-class Meta {
-  static eval(source) {
-    if (!(source is String)) Fiber.abort("Source code must be a string.")
-
-    var fn = compile_(source)
-    // TODO: Include compile errors.
-    if (fn == null) Fiber.abort("Could not compile source code.")
-
-    Fiber.new(fn).call()
-  }
-
-  foreign static compile_(source)
-}