test: the attacker the device suite never had

The audit's sharpest finding was structural, not a bug: a fully green suite
had hidden six real defects because it contains no attacker. Every device
case asserts that a driver handed its own hardware can drive it. None asked
what a process handed NOTHING can do.

device-authority-test is that process. It is spawned with no device and
asserts what it therefore cannot do: it cannot give away a device another
task holds, nor a free one, because the kernel's rule is that you may give
away what you hold and the device's state is irrelevant to a process holding
nothing. Asserted across every device the machine actually has, so it cannot
pass by accident of which one happened to be free at boot — six on QEMU,
none of them its.

A positive control runs first. device_enumerate works from this process, so
the refusals below it are decisions rather than a syscall path that is
simply broken here; without it, "everything failed" would read identically
to "the assertions are meaningless". A nonexistent device is refused as
NoSuchDevice rather than NotHeld, because a refusal that cannot name its own
rule is what cost a debugging session on the Ryzen.

What it deliberately does not assert, and says so in its header:
device_claim is still first-come-first-served at this point in the run. That
is the hole D6 closes, and the claim half of the invariant joins this
fixture then. Asserting it now would be writing a test that documents the
bug.

Verified to discriminate: removing the holder check flips "every transfer by
a non-holder is refused" while the positive control keeps passing.

Suite 117 -> 118.

build.zig.zon

@@ -79,6 +79,7 @@
         .@"protocol-registry-test" = .{ .path = "test/system/services/protocol-registry-test", .lazy = true },
         .@"protocol-denied-test" = .{ .path = "test/system/services/protocol-denied-test", .lazy = true },
         .@"protocol-conformance-test" = .{ .path = "test/system/services/protocol-conformance-test", .lazy = true },
+        .@"device-authority-test" = .{ .path = "test/system/services/device-authority-test", .lazy = true },
         // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
         //.example = .{
         //    // When updating this field to a new URL, be sure to delete the corresponding