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.

org/modern-backend.org

@@ -652,16 +652,18 @@ compatibility across SBCL versions. Returns (values cols rows).
 
 #+BEGIN_SRC lisp :tangle ../src/backend/modern.lisp
 (defmethod backend-size ((b modern-backend))
-  (let* ((+tiocgwinsz+ 21523)  ; 0x5413 on Linux
-         (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
-    (unwind-protect
-         (progn
-           (sb-unix:unix-ioctl (sb-sys:fd-stream-fd (backend-output-stream b))
-                               +tiocgwinsz+
-                               (sb-alien:alien-sap winsize))
-           (values (sb-alien:deref winsize 1)  ;; cols
-                   (sb-alien:deref winsize 0))) ;; rows
-      (sb-alien:free-alien winsize))))
+  (or (ignore-errors
+        (let* ((+tiocgwinsz+ 21523)  ; 0x5413 on Linux
+               (winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
+          (unwind-protect
+               (progn
+                 (sb-unix:unix-ioctl (sb-sys:fd-stream-fd (backend-output-stream b))
+                                     +tiocgwinsz+
+                                     (sb-alien:alien-sap winsize))
+                 (values (sb-alien:deref winsize 1)  ;; cols
+                         (sb-alien:deref winsize 0))) ;; rows
+            (sb-alien:free-alien winsize))))
+      (values 80 24)))
 #+END_SRC
 
 ** Capability query and write
@@ -703,8 +705,9 @@ calls --- one =backend-write= per draw operation --- by packing everything
 into one buffer.
 
 #+BEGIN_SRC lisp :tangle ../src/backend/modern.lisp
-(defmethod draw-text ((b modern-backend) x y string fg bg
-                      &key bold italic underline reverse dim blink)
+ (defmethod draw-text ((b modern-backend) x y string fg bg
+                       &key bold italic underline reverse dim blink
+                       &allow-other-keys)
   (let ((parts (list (cursor-move-escape x y)
                      (sgr-fg fg) (sgr-bg bg)
                      (when bold (sgr-attr :bold))