Add prelude and while macro

This commit introduces a new prelude file that defines the `while` macro
and registers it during environment bootstrapping. The `again` macro has
been updated to accept multiple arguments for its recursive call, and
several examples have been adjusted to reflect this change.
Additionally, the `MacroRegistry` in the compiler is now cloneable and
can be moved out of the `MacroExpander`.

src/ast/rtl/prelude.myc

@@ -0,0 +1,9 @@
+;; Myc Prelude
+;; This file is evaluated during Environment bootstrapping.
+;; It contains standard macros and functions.
+
+(macro while [cond body]
+  `((fn [] (if ~cond
+             (do ~body (again))
+           )))
+)