ps2: one instance, every node the machine has

The 8042 is a single controller described by two ACPI nodes — PNP0303
carries the 0x60/0x64 ports, PNP0F13 is the mouse — so it cannot be split
across two processes without them fighting over the same registers. That is
why ps2-bus is a singleton, and why it used to find and claim both nodes
itself.

The manager now gives it every matching node instead. The keyboard node
rides the spawn, because it holds the ports and is needed immediately; the
mouse node is transferred to the already-running instance. Late arrival is
safe here and the ordering is natural rather than lucky: the mouse is not
touched until after the controller handshakes and identify. Measured, the
handover lands at 0.336 and the driver reaches the mouse at 0.456.

Because the count is however many matched, a machine with no PS/2 ports or
only one works without a special case — which matters, since the bus is
mostly emulated now and machines vary.

ps2-bus claims nothing. irq_bind on the mouse node is the proof it holds it:
that call is ownership-gated, so a failure means the handover did not land
rather than a hardware fault, and the log says so.

acpi-ps2 asserts both delegations with the spawned device backreferenced, so
the node that rides the spawn must be the one the driver was spawned for.
Disabling the second delegation fails it.

Two things worth recording. The first discrimination patch was not valid Zig,
so nothing ran and a stale binary reported a pass — checked the build before
believing it. And with the second delegation disabled, acpi-ps2 fails while
input still passes: the mouse works without its IRQ binding, so exactly one
case covers that path.

Suite 118/118.

test/qemu_test.py

@@ -780,8 +780,16 @@ CASES = [
     {"name": "acpi-ps2",
      "smp":    4,
      "timeout": 150,
+     # The 8042 is ONE controller described by two ACPI nodes, so the single ps2-bus
+     # instance must receive BOTH. The keyboard node rides the spawn — it carries the
+     # 0x60/0x64 ports and is needed immediately — and the mouse node is transferred to
+     # the already-running instance, which is safe because it is not touched until after
+     # the controller handshakes and identify. Two processes cannot split this: they
+     # would fight over the same registers.
      "expect": r"discovery: device \d+\s+bus=acpi hid=PNP0303[\s\S]*"
-               r"device-manager: spawned \S*ps2-bus[\s\S]*"
+               r"device-manager: delegated device (\d+) to \S*ps2-bus[\s\S]*"
+               r"device-manager: spawned \S*ps2-bus for device \1[\s\S]*"
+               r"device-manager: delegated device \d+ to \S*ps2-bus \(already running\)[\s\S]*"
                r"ps2-bus: keyboard driver attached",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # M21.1: the SCI + power button. Boot the manager (which spawns the acpi