reorg: move device-manager-protocol to library/protocol + direct import

device-manager-protocol -> library/protocol/device-manager/. Its consumers
(pci-bus, usb-xhci-bus, the acpi discovery service, device-manager, device-list,
crash-test, and the not-yet-built intel-integrated display sub-driver) import the
module directly instead of through runtime.device_manager_protocol, which is
deleted. runtime.device_manager (the hello client) already imported the module
by name and is unchanged.

zig build + test green; device-manager, driver-restart, device-list, pci-scan pass.

system/services/device-list/device-list.zig

@@ -6,7 +6,7 @@
 
 const std = @import("std");
 const runtime = @import("runtime");
-const protocol = runtime.device_manager_protocol;
+const protocol = @import("device-manager-protocol");
 
 fn writeLine(comptime fmt: []const u8, arguments: anytype) void {
     var line: [96]u8 = undefined;