controller: fix bogus timer implementation

The previous version was using wall clock time for the timer because I
am an idiot. During time syncs or possibly due to other reasons, this
could jump backwards and cause an overflow. This obviously needed a
monotonic clock source, and now it has one.

src/YaesuController.zig

@@ -355,7 +355,7 @@ const Controller = struct {
     fn run(self: *Controller) !void {
         self.current_state = .initializing;
 
-        var timer: LoopTimer = .{ .interval_ns = config.controller.loop_interval_ns };
+        var timer = LoopTimer.init(config.controller.loop_interval_ns);
 
         while (timer.mark()) : (timer.sleep()) {
             self.updateFeedback() catch {
@@ -416,18 +416,22 @@ const Controller = struct {
 
 pub const LoopTimer = struct {
     interval_ns: u64,
+    timer: std.time.Timer,
 
-    start: i128 = 0,
+    pub fn init(interval_ns: u64) LoopTimer {
+        return .{
+            .interval_ns = interval_ns,
+            .timer = std.time.Timer.start() catch @panic("Could not create timer"),
+        };
+    }
 
     pub fn mark(self: *LoopTimer) bool {
-        self.start = std.time.nanoTimestamp();
+        self.timer.reset();
         return true;
     }
 
     pub fn sleep(self: *LoopTimer) void {
-        const now = std.time.nanoTimestamp();
-        const elapsed: u64 = @intCast(now - self.start);
-
-        std.time.sleep(self.interval_ns - elapsed);
+        const elapsed = self.timer.read();
+        std.time.sleep(self.interval_ns -| elapsed);
     }
 };