Let a test declare the controller mode it needs; the runner switches to it

The cloud job tests enter cloud mode and stay there, by design, so a
queue (or an operator) that goes on to a motion test reaches it with
gfcloud as the controller and no grblHAL process to find:
motion.step-timing-under-load failed on exactly that, before it touched
the machine. Nothing in the runner put the machine into the mode a test
needed; the baseline only preserved the mode it found.

A test now declares `mode="grbl"` (or "cloud") in @test. The runner's pre
pass, after the leftovers are handled and before the preserved state is
captured, switches through POST /mode, waits for the supervisor to settle
(controller running, motion verified) and for the Grbl port to answer,
and fails the test with the reason when the mode cannot be established.
Capturing after the switch means the post pass keeps the mode the test
asked for, so the machine changes mode only where the next test asks for
it and never between tests of the same mode. The cloud job tests keep
managing their own entry (enter_cloud also waits for the service
session) and declare nothing.

Tagged: every motion.* test but the mode-agnostic liveness probe, the six
laser.* tests, cooling.fans-quiet-after-motion, cloud.mode-switch and
cloud.gfhome-homing (both start in GRBL mode). controller_pid() now says
what mode forgectrl reports when the process is missing. The page shows
the declared mode as a badge; the Grbl port probe moved to hw.

Proof: tests/test_mode.py (switch_mode against the fake forgectrl,
including a refused switch, a controller that never comes up and a port
that never opens; the runner end to end from cloud mode, from grbl mode,
an undeclared test, and a failed switch). 151 unit tests pass; the
coverage lint is clean. No catalog consequence beyond the suite modules'
own source hashes: the change is to how a test is started, not to what
it proves.

forgetest/tests/helpers.py

@@ -69,9 +69,9 @@ def _noop(ctx):
     pass
 
 
-def make_test(id, covers, always=False, requires=(), kind="auto", fn=None, subsystem=None):
+def make_test(id, covers, always=False, requires=(), kind="auto", fn=None, subsystem=None, mode=None):
     return catalog_mod.Test(id, "Title " + id, subsystem or id.split(".")[0], kind, "api",
-                            covers, requires, always, 1, (), "desc", fn or _noop)
+                            covers, requires, always, 1, (), "desc", fn or _noop, mode=mode)
 
 
 def registry(*tests):