Loops: :finish, :abandon, :while, :until and the :subloop form

The clause table, stopping early and nesting use the new names, and
count-lines uses :until instead of a counter that only drove the loop.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-5-5)

Co-Authored-By: eca-agent <git@eca.dev>

_02_.Writing-programs.sz

@@ -500,8 +500,8 @@ To avoid leaking resources, you will usually want to use @code{call-with-input-f
 (defun (count-lines path)
   (call-with-input-file path
     (fun (port)
-      (loop (:for i (up-from 0))
-            (:break-let (Some line) (read-line/opt port))
+      (loop (:until (port-eof? port))
+            (:let line (read-line port))
             (:acc lines (counting line))
             => lines))))