Update is-callable to also check builtins

Fixes #1037

modules/helper/init.zsh

@@ -12,7 +12,7 @@ function is-autoloadable {
 
 # Checks if a name is a command, function, or alias.
 function is-callable {
-  (( $+commands[$1] )) || (( $+functions[$1] )) || (( $+aliases[$1] ))
+  (( $+commands[$1] || $+functions[$1] || $+aliases[$1] || $+builtins[$1] ))
 }
 
 # Checks a boolean variable for "true".