tray_test.py and motion.tray: the crumb tray's mode on the null-sink controller and on the machine

- scripts/bench/tray_test.py, run by the driver's CI: M103 P1 and P0
  move Z and its envelope by tray_offset_mm on the lens step grid, tell
  the sender, write and remove the marker beside the shared config, and
  ship no step; a missing P, P2, P0.5, P-1, and an axis word are errors
  that change nothing; the switch behind a move waits for the move; the
  port's tray op with a sender connected, its count exact, refused out of
  form, during a program, and at a package's M-code; the mode across a
  soft reset and a killed controller, a start over the marker taking the
  lens reference in the tray-out frame; the offset's range; an
  unreferenced lens; a camera home in both modes handing the runner the
  same park. The kernel-idle half of the barrier needs the pulse device:
  a null sink is always idle.
- scripts/bench/ctlport_test.py: the dark case carries tray out and in
  under an open armed window.
- forgetest: motion.tray in its own module, suite/tray.py, so no other
  test's fingerprint moves. It switches the mode both ways through the
  panel's route and through M103 from a Grbl client and judges each
  switch: /status's mode, Z, and reach moved by the offset's grid, the
  port's state, the marker, the reference and its source unchanged, the
  client told, the kernel's counters unmoved. A jog to the Z the lens
  read before a switch is refused in the other mode and taken back in
  the mode found; a setup card started with the tray out is refused in
  the operator's words; the panel page carries the switch. The mode goes
  back as found in a finally. It does not restart the controller, which
  would drop the X and Y reference: persistence is tray_test.py's.
- The bench registry and README list tray_test.py.

Proof: tray_test.py ALL PASS against the driver with the mode, and six
driver copies each missing one part of it fail. The driver's whole CI
harness list passes. The forgetest unit suite: 500 tests OK. The
coverage lint over the working trees: nothing uncovered, 126 tests. On
the bench reference, with the binaries hot-deployed on the fx18 image:
motion.tray PASS, and FAIL against the driver whose anchor lost its
source word on the second switch.

Acceptance. motion.tray is new; the suite and bench files are in no
other test's fingerprint.

scripts/bench/ctlport_test.py

@@ -33,8 +33,8 @@ job after it.
   8. the port's client is the dead-man: closing it cancels its jog
   9. every port operation ships dark. Under an open armed window, with M3
      modal and S above zero, a port jog, a canceled port jog, the refused
-     jogs, and the panel operations add steps to the shipped stream and not
-     one FIRE tick. A jog block carries the modal spindle state, so the
+     jogs, and the panel operations (the tray's mode among them) add steps
+     to the shipped stream and not one FIRE tick. A jog block carries the modal spindle state, so the
      stream's mask on jogging is the only thing that keeps a jog dark, and
      this is what holds the port to it
  10. "sender out" keeps senders from the network out, and only on an idle
@@ -593,6 +593,8 @@ def test_port_dark():
         replies["release"] = s.port.request("release")      # refused: a laser job is armed
         replies["energize"] = s.port.request("energize")
         replies["home"] = s.port.request("home")            # manual: declares X0 Y0, moves nothing
+        replies["tray out"] = s.port.request("tray out")    # the Z frame moves, the head does not
+        replies["tray in"] = s.port.request("tray in")
         replies["jog-after-home"] = s.port.request("jog G91 X6 F1200")
         s.sender.wait_state("Idle")
         time.sleep(0.5)
@@ -600,6 +602,8 @@ def test_port_dark():
         steps1, fire1 = s.ticks()
         if replies["jog"] != "ok" or replies["jog-long"] != "ok" or replies["jog-after-home"] != "ok":
             fail("[dark] a port jog under the open window was refused: %r" % replies)
+        if replies["tray out"] != "ok" or replies["tray in"] != "ok":
+            fail("[dark] the tray op under the open window was refused: %r" % replies)
         if steps1 <= steps0:
             fail("[dark] the port jogs shipped no step: the case would prove nothing")
         if s.sender.saw("laser disarmed"):