VR keyboard bridge: adaptive sampling, on demand only without touch typing

The controller bridge reads the poses with setTimeout instead of a fixed
11 ms interval: the next read after (distance - 10 cm) / 2.5 m/s, 11-250 ms,
the distance being the nearest tip's to the keyboard's rect plus a margin,
so a hand up to 2.5 m/s is read within 10 cm before it reaches the surface
(the tracker's crossing and 8 cm jump guard see 11 ms steps as before).
Full rate during a demand or with a pulled trigger. Without touch typing
(controllers.continuous, set by vr-keyboard-touch) no reads while the
keyboard is shown until a swipe demands them; a demand starting reads at
once. Bridge VERSION 6. Tests with a fake clock: bridge.test.mjs.

modules/vr-keyboard-touch.nix

@@ -2,7 +2,7 @@
 # key is pressed when a controller's tip (where SteamVR's laser starts)
 # passes through it. Independent of keyboard.vr.enable / extraKeys.
 # - The tips relative to the keyboard come from the controller bridge
-#   (vr-keyboard-controllers.nix, turned on here).
+#   (vr-keyboard-controllers.nix, turned on here, sampling continuously).
 # - vr-keyboard-touch/keyboard-patch.js (Steam UI, 8080; patch
 #   "vr-keyboard-touch"): tracker.js per hand (contact, hysteresis); presses
 #   the key with the keyboard's own touch handlers, like a laser press.
@@ -36,6 +36,7 @@ in {
 
   config = lib.mkIf cfg.enable {
     steamFrame.keyboard.vr.controllers.enable = true;
+    steamFrame.keyboard.vr.controllers.continuous = true;
     steamFrame.uiPatches.patches = [ {
       name = "vr-keyboard-touch";
       target.title = "SharedJSContext";