core: move system contents and remove dir

core/System.zig

@@ -1,7 +1,18 @@
 const std = @import("std");
 
 // TODO: Add storage interface.
-pub const Clock = @import("system/Clock.zig");
+
+pub const Clock = struct {
+    const Self = @This();
+
+    ptr: *anyopaque,
+    monotonicMicrosFn: *const fn (ptr: *anyopaque) u64,
+
+    pub fn monotonicMicros(self: *Self) u64 {
+        return self.monotonicMicrosFn(self.ptr);
+    }
+};
+
 pub const Rng = std.Random;
 
 clock: Clock,

core/system/Clock.zig

@@ -1,8 +0,0 @@
-const Self = @This();
-
-ptr: *anyopaque,
-monotonicMicrosFn: *const fn (ptr: *anyopaque) u64,
-
-pub fn monotonicMicros(self: *Self) u64 {
-    return self.monotonicMicrosFn(self.ptr);
-}