Rename @zag-js/checkbox to @zag-js/timer to fix typo (#2296)

Rename `@zag-js/checkbox` to `@zag-js/timer`

Author: baseplate-admin

packages/machines/timer/README.md

@@ -1,6 +1,6 @@
-# @zag-js/checkbox
+# @zag-js/timer
 
-Core logic for the checkbox widget implemented as a state machine
+Core logic for the timer widget implemented as a state machine
 
 ## **Installation**