apl: Phase 3 take ↑ / drop ↓ / rotate ⌽⊖ — 50/50 tests green

Add apl-take (dyadic ↑, multi-axis, cycling pad), apl-drop (dyadic ↓),
apl-reverse (monadic ⌽), apl-rotate (dyadic ⌽, last axis),
apl-reverse-first (monadic ⊖), apl-rotate-first (dyadic ⊖, first axis),
apl-safe-mod helper for negative rotation arithmetic.

23 new tests in lib/apl/tests/structural.sx.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/apl/tests/structural.sx

@@ -188,4 +188,138 @@
     (apl-transpose-dyadic
       (make-array (list 3) (list 2 1 3))
       (make-array (list 2 3 4) (range 0 24))))
-  (list 3 2 4))
+  (list 3 2 4))
+
+(apl-test
+  "take 3 from front"
+  (rv (apl-take (apl-scalar 3) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 1 2 3))
+
+(apl-test
+  "take 0"
+  (rv (apl-take (apl-scalar 0) (make-array (list 5) (list 1 2 3 4 5))))
+  (list))
+
+(apl-test
+  "take -2 from back"
+  (rv (apl-take (apl-scalar -2) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 4 5))
+
+(apl-test
+  "take over-take pads with 0"
+  (rv (apl-take (apl-scalar 7) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 1 2 3 4 5 0 0))
+
+(apl-test
+  "take matrix 1 row 2 cols shape"
+  (sh
+    (apl-take
+      (make-array (list 2) (list 1 2))
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 1 2))
+
+(apl-test
+  "take matrix 1 row 2 cols ravel"
+  (rv
+    (apl-take
+      (make-array (list 2) (list 1 2))
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 1 2))
+
+(apl-test
+  "take matrix negative row"
+  (rv
+    (apl-take
+      (make-array (list 2) (list -1 3))
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 4 5 6))
+
+(apl-test
+  "drop 2 from front"
+  (rv (apl-drop (apl-scalar 2) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 3 4 5))
+
+(apl-test
+  "drop -2 from back"
+  (rv (apl-drop (apl-scalar -2) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 1 2 3))
+
+(apl-test
+  "drop all"
+  (rv (apl-drop (apl-scalar 5) (make-array (list 5) (list 1 2 3 4 5))))
+  (list))
+
+(apl-test
+  "drop 0"
+  (rv (apl-drop (apl-scalar 0) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 1 2 3 4 5))
+
+(apl-test
+  "drop matrix 1 row shape"
+  (sh
+    (apl-drop
+      (make-array (list 2) (list 1 0))
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 1 3))
+
+(apl-test
+  "drop matrix 1 row ravel"
+  (rv
+    (apl-drop
+      (make-array (list 2) (list 1 0))
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 4 5 6))
+
+(apl-test
+  "reverse vector"
+  (rv (apl-reverse (make-array (list 5) (list 1 2 3 4 5))))
+  (list 5 4 3 2 1))
+
+(apl-test
+  "reverse scalar identity"
+  (rv (apl-reverse (apl-scalar 42)))
+  (list 42))
+
+(apl-test
+  "reverse matrix last axis"
+  (rv (apl-reverse (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 3 2 1 6 5 4))
+
+(apl-test
+  "reverse-first matrix"
+  (rv (apl-reverse-first (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 4 5 6 1 2 3))
+
+(apl-test
+  "reverse-first vector identity"
+  (rv (apl-reverse-first (make-array (list 4) (list 1 2 3 4))))
+  (list 4 3 2 1))
+
+(apl-test
+  "rotate vector left by 2"
+  (rv (apl-rotate (apl-scalar 2) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 3 4 5 1 2))
+
+(apl-test
+  "rotate vector right by 1 (negative)"
+  (rv (apl-rotate (apl-scalar -1) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 5 1 2 3 4))
+
+(apl-test
+  "rotate by 0 is identity"
+  (rv (apl-rotate (apl-scalar 0) (make-array (list 5) (list 1 2 3 4 5))))
+  (list 1 2 3 4 5))
+
+(apl-test
+  "rotate matrix last axis"
+  (rv
+    (apl-rotate (apl-scalar 1) (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 2 3 1 5 6 4))
+
+(apl-test
+  "rotate-first matrix"
+  (rv
+    (apl-rotate-first
+      (apl-scalar 1)
+      (make-array (list 2 3) (list 1 2 3 4 5 6))))
+  (list 4 5 6 1 2 3))