Revert "refactor: time -> clock"

This reverts commit 44cf08e57c.

src/kern/private.zig

@@ -20,7 +20,7 @@ pub const log = @import("log.zig");
 pub const cpu = @import("cpu.zig");
 pub const thread = @import("thread.zig");
 pub const dpc = @import("dpc.zig");
-pub const clock = @import("clock.zig");
+pub const time = @import("time.zig");
 pub const sched = @import("sched.zig");
 pub const wait = @import("wait.zig");
 pub const timer = @import("timer.zig");