fix: add draw-text method for raw 2D arrays

Application code (passepartout TUI) calls draw-text with a framebuffer
(2D array) as the first argument, but draw-text only had methods for
framebuffer-backend CLOS instances. Added a method on array that sets
cells directly on the framebuffer array, matching make-framebuffer's
return type.

src/backend/simple.lisp

@@ -32,9 +32,10 @@
     (length string)))
 
 (defmethod draw-text ((b simple-backend) x y string fg bg
-                      &key bold italic underline reverse dim blink)
-  (declare (ignore x y fg bg bold italic underline reverse dim blink))
-  (backend-write b string))
+                      &key bold italic underline reverse dim blink
+                      &allow-other-keys)
+ (declare (ignore x y fg bg bold italic underline reverse dim blink))
+ (backend-write b string))
 
 (defun %simple-border-char (pos)
   "Return ASCII border character at POS.