lang/common-lisp: sly-eval-region = eval handler

This allows you to use the `gr` operator to evaluate code on-the-fly.

modules/lang/common-lisp/config.el

@@ -13,6 +13,7 @@
       ("^\\*sly-traces"      :vslot 6 :ttl nil)))
 
   (set-repl-handler! 'lisp-mode #'sly-mrepl)
+  (set-eval-handler! 'lisp-mode #'sly-eval-region)
   (set-lookup-handlers! 'lisp-mode
     :definition #'sly-edit-definition
     :documentation #'sly-describe-symbol)