[client] cursor: pace composited redraws

Coalesce pointer updates to the nominal output cadence instead of
waking the renderer for every transport packet. Keep request and
presented generations separate so updates racing a render receive a
trailing swap.

Let JIT consume cursor changes on display callbacks to preserve VRR
cadence, and use a deadline worker for non-JIT rendering. Give normal
source frames a short grace period so an on-rate feed absorbs the
cursor update instead of producing an extra swap.

Repaint visibility and cursor-content changes even when movement
redraws are disabled, including the transition that hides the cursor.

client/src/config.c

@@ -398,7 +398,7 @@ static struct Option options[] =
   {
     .module         = "input",
     .name           = "mouseRedraw",
-    .description    = "Mouse movements trigger redraws (ignores FPS minimum)",
+    .description    = "Mouse movements trigger display-rate redraws",
     .type           = OPTION_TYPE_BOOL,
     .value.x_bool   = true,
   },