HS: parser+compiler — toggle for-in lookahead, throttled/debounced modifiers (-2 skips)

parser.sx parse-toggle-cmd: when seeing 'toggle .foo for', peek the
following two tokens. If they are '<ident> in', it is a for-in loop
and toggle does NOT consume 'for' as a duration clause. Restores the
trailing for-in to the command list.

parser.sx parse-on (handler modifiers): recognize 'throttled at <ms>'
and 'debounced at <ms>' as handler modifiers. Captured as :throttle /
:debounce kwargs in the on-form parts list.

compiler.sx emit-on: pre-extract :throttle / :debounce from parts via
new _strip-throttle-debounce helper before scan-on, then wrap the built
handler with (hs-throttle! handler ms) or (hs-debounce! handler ms).

runtime.sx: hs-throttle! — closure with __hs-last-fire timestamp,
fires immediately and drops events arriving within ms of the last fire.
hs-debounce! — closure with __hs-timer, clears any pending timer and
schedules a new setTimeout(handler, ms) so only the last burst event
fires.

Both formerly-architectural skips now pass:
- "toggle does not consume a following for-in loop"
- "throttled at <time> drops events within the window"

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

spec/tests/test-hyperscript-behavioral.sx

@@ -10036,8 +10036,10 @@
       (dom-set-attr _el-d "_" "on click throttled at 200ms then increment @n then put @n into me")
       (dom-append (dom-body) _el-d)
       (hs-activate! _el-d)
-      (assert= (dom-text-content (dom-query-by-id "d")) "1")
-    ))
+      (dom-dispatch _el-d "click" nil)
+      (dom-dispatch _el-d "click" nil)
+      (assert= (dom-text-content (dom-query-by-id "d")) "1"))
+  )
   (deftest "uncaught exceptions trigger 'exception' event"
     (hs-cleanup!)
     (let ((_el-button (dom-create-element "button")))
@@ -13867,7 +13869,19 @@ end")
       (assert= (dom-text-content _out) "2"))
   )
   (deftest "toggle does not consume a following for-in loop"
-    (error "SKIP (untranslated): toggle does not consume a following for-in loop"))
+    (hs-cleanup!)
+    (let ((_out (dom-create-element "div")) (_btn (dom-create-element "div")))
+      (dom-set-attr _out "id" "out")
+      (dom-set-attr _btn "id" "btn")
+      (dom-set-attr _btn "_" "on click toggle .foo for x in [1, 2, 3] put x into #out end")
+      (dom-append (dom-body) _out)
+      (dom-append (dom-body) _btn)
+      (hs-activate! _btn)
+      (assert (not (dom-has-class? _btn "foo")))
+      (dom-dispatch _btn "click" nil)
+      (assert (dom-has-class? _btn "foo"))
+      (assert= (dom-text-content _out) "3"))
+  )
 )
 
 ;; ── transition (17 tests) ──