C2: migrate consumers off the runtime shim to direct concern-module imports

Every user binary and the two device-logic library modules (pci, usb) now
`@import` the concern modules directly instead of aliasing through `runtime`:

  runtime.ipc/process/time/service/input/block/display  -> @import("<module>")
  runtime.device / runtime.device_manager               -> @import("driver")
  runtime.fs                                             -> @import("file-system")
  runtime.Thread                                         -> @import("thread").Thread
  runtime.system.{write,writeRecord,klog*}              -> logging.*
  runtime.system.{sleep,timerOnce,wallClock,clock}     -> time.*
  runtime.system.{spawn*,kill,exit,yield,processes,...}-> process.*
  runtime.system.{mmap,munmap,PROT_*}                  -> memory.*
  runtime.dma.* / runtime.shared_memory.* / runtime.allocator -> memory.*

Each consumer keeps its own alias name (e.g. `const device = @import("driver")`),
so call sites are unchanged and there are no collisions with local `driver`
variables. build.zig now injects the concern modules into every user binary via
`default_imports`; pci/usb module import lists were updated to match.

The `runtime` and `system` shims remain for one more step (root.zig still uses
runtime); they are deleted in C5. Nothing but root.zig imports `runtime` now.

Verified: zig build, zig build test, and 17 QEMU cases (smoke, device-manager,
logger, fat-mount, fat-mutations, usb-storage, usb-hid, display-native,
virtio-gpu, input, thread-spawn, thread-mutex, process-kill, shared-memory,
driver-restart, acpi-ps2, pci-scan).

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

@@ -5,23 +5,25 @@
 //! device_* system call.
 
 const std = @import("std");
-const runtime = @import("runtime");
+const ipc = @import("ipc");
+const time = @import("time");
+const logging = @import("logging");
 const device_manager_protocol = @import("device-manager-protocol");
 
 fn writeLine(comptime fmt: []const u8, arguments: anytype) void {
     var line: [96]u8 = undefined;
-    _ = runtime.system.write(std.fmt.bufPrint(&line, fmt, arguments) catch return);
+    _ = logging.write(std.fmt.bufPrint(&line, fmt, arguments) catch return);
 }
 
 pub fn main() void {
-    var manager: ?runtime.ipc.Handle = null;
+    var manager: ?ipc.Handle = null;
     var tries: u32 = 0;
     while (manager == null and tries < 200) : (tries += 1) {
-        manager = runtime.ipc.lookup(.device_manager);
-        if (manager == null) runtime.system.sleep(20);
+        manager = ipc.lookup(.device_manager);
+        if (manager == null) time.sleepMillis(20);
     }
     const h = manager orelse {
-        _ = runtime.system.write("device-list: no device manager\n");
+        _ = logging.write("device-list: no device manager\n");
         return;
     };
 
@@ -33,12 +35,12 @@ pub fn main() void {
     tries = 0;
     while (tries < 20) : (tries += 1) {
         const request = device_manager_protocol.Enumerate{};
-        length = runtime.ipc.call(h, std.mem.asBytes(&request), &reply) catch 0;
+        length = ipc.call(h, std.mem.asBytes(&request), &reply) catch 0;
         if (length >= @sizeOf(device_manager_protocol.EnumerateReply)) {
             count = std.mem.bytesToValue(device_manager_protocol.EnumerateReply, reply[0..@sizeOf(device_manager_protocol.EnumerateReply)]).count;
             if (count != 0) break;
         }
-        runtime.system.sleep(100);
+        time.sleepMillis(100);
     }
     writeLine("device-list: {d} devices\n", .{count});
     var offset: usize = @sizeOf(device_manager_protocol.EnumerateReply);
@@ -51,20 +53,20 @@ pub fn main() void {
 
     // The subscription: our endpoint rides as the call's capability; events
     // arrive as buffered messages carrying the same structs the bus sends.
-    const endpoint = runtime.ipc.createIpcEndpoint() orelse {
-        _ = runtime.system.write("device-list: no endpoint\n");
+    const endpoint = ipc.createIpcEndpoint() orelse {
+        _ = logging.write("device-list: no endpoint\n");
         return;
     };
     const subscribe = device_manager_protocol.Subscribe{};
-    _ = runtime.ipc.callCap(h, std.mem.asBytes(&subscribe), &reply, endpoint) catch {
-        _ = runtime.system.write("device-list: subscribe failed\n");
+    _ = ipc.callCap(h, std.mem.asBytes(&subscribe), &reply, endpoint) catch {
+        _ = logging.write("device-list: subscribe failed\n");
         return;
     };
-    _ = runtime.system.write("device-list: subscribed\n");
+    _ = logging.write("device-list: subscribed\n");
 
     var receive: [device_manager_protocol.message_maximum]u8 = undefined;
     while (true) {
-        const got = runtime.ipc.replyWait(endpoint, &.{}, &receive, null);
+        const got = ipc.replyWait(endpoint, &.{}, &receive, null);
         if (!got.isMessage() or got.len < 1) continue;
         switch (receive[0]) {
             @intFromEnum(device_manager_protocol.Operation.child_added) => {