Fix O(n^2) performance bug in uniqArr; avoid duplicate keyF evaluations (#575)

This PR implements two performance optimizations in `uniqueArr`:

- **Fix an O(n^2) performance bug**:
#564 changed this code to
call `out.result()` on every loop iteration, resulting in copying of an
`O(n)` sized array on each loop iteration. We can avoid this by keeping
a reference to the last output element.
- **Avoid duplicate keyF evaluations**: in the old code, each loop
iteration would repeat the `keyF` evaluation for the last element of the
output array; the new code calls `keyF` exactly once per element by
maintaining a `lastAddedKey` variable during the loop.
- This is similar in spirit to
#245

Claude (Opus 4.5) spotted the O(n^2) bug and designed that part of the
fix. I spotted the duplicate keyF evaluation and suggested this fix
(plus the switch to a `while` loop).

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: JoshRosen

sjsonnet/src/sjsonnet/stdlib/SetModule.scala

@@ -65,22 +65,19 @@ object SetModule extends AbstractFunctionModule {
     val out = new mutable.ArrayBuilder.ofRef[Lazy]
     // Set a reasonable size hint - in the worst case (no duplicates), we'll need arrValue.length elements
     out.sizeHint(arrValue.length)
-    for (v <- arrValue) {
-      val outResult = out.result()
-      if (outResult.length == 0) {
+
+    var lastAddedKey: Val = null
+    var i = 0
+    while (i < arrValue.length) {
+      val v = arrValue(i)
+      val vKey =
+        if (keyF.isInstanceOf[Val.False]) v.force
+        else keyF.asInstanceOf[Val.Func].apply1(v, pos.noOffset)(ev, TailstrictModeDisabled)
+      if (lastAddedKey == null || !ev.equal(vKey, lastAddedKey)) {
         out.+=(v)
-      } else if (keyF.isInstanceOf[Val.False]) {
-        if (!ev.equal(outResult.last.force, v.force)) {
-          out.+=(v)
-        }
-      } else if (!keyF.isInstanceOf[Val.False]) {
-        val keyFFunc = keyF.asInstanceOf[Val.Func]
-        val o1Key = keyFFunc.apply1(v, pos.noOffset)(ev, TailstrictModeDisabled)
-        val o2Key = keyFFunc.apply1(outResult.last, pos.noOffset)(ev, TailstrictModeDisabled)
-        if (!ev.equal(o1Key, o2Key)) {
-          out.+=(v)
-        }
+        lastAddedKey = vKey
       }
+      i += 1
     }
 
     Val.Arr(pos, out.result())