search: did-you-mean spelling suggestion + 9 tests

suggest/suggestN rank indexed terms by edit distance to a (misspelled) query
term, alphabetical tiebreak. 234/234.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/tests/suggest.sx

@@ -0,0 +1,42 @@
+;; Extension — did-you-mean / spelling suggestion.
+;; Corpus terms (sorted): ample apple apply banana orange
+
+(define
+  suggest-setup
+  "idx = indexDoc 1 \"apple apply ample banana orange\" emptyIndex\n")
+
+(define
+  suggest-cases
+  (list
+    (list "suggest exact term" "[suggest \"apple\" idx]" (list "apple"))
+    (list
+      "suggest misspelled banana"
+      "[suggest \"bananna\" idx]"
+      (list "banana"))
+    (list
+      "suggest missing letter orange"
+      "[suggest \"orang\" idx]"
+      (list "orange"))
+    (list "suggest closest apply" "[suggest \"aply\" idx]" (list "apply"))
+    (list "suggestN 1 banana" "suggestN 1 \"bananna\" idx" (list "banana"))
+    (list
+      "suggestN 2 ties alpha"
+      "suggestN 2 \"aple\" idx"
+      (list "ample" "apple"))
+    (list "suggest empty term shortest" "[suggest \"\" idx]" (list "ample"))
+    (list "suggest empty index" "[suggest \"apple\" emptyIndex]" (list ""))
+    (list "suggestN empty index" "suggestN 1 \"apple\" emptyIndex" (list))))
+
+(define
+  suggest-results
+  (search-batch
+    suggest-setup
+    (map (fn (c) (nth c 1)) suggest-cases)))
+
+(map-indexed
+  (fn
+    (i c)
+    (hk-test (nth c 0) (nth suggest-results i) (nth c 2)))
+  suggest-cases)
+
+{:fail hk-test-fail :pass hk-test-pass :fails hk-test-fails}