feat: log tick/idle diagnostics in example server

Brackets game_tick() with skele_clock_tick_begin/end and the
sleep-to-hit-tick-rate call with skele_clock_idle_begin/end.

src/server/main.c

@@ -2,6 +2,7 @@
 #include <skele/clock.h>
 #include <skele/skele.h>
 #include <stk/stk.h>
+#include <stk/stk_log.h>
 
 static uint8_t running = 1;
 
@@ -11,6 +12,7 @@ int main(int argc, char *argv[])
 {
 	uint64_t tick_start;
 	uint64_t elapsed;
+	uint64_t last_print = 0;
 
 	(void)argc;
 	(void)argv;
@@ -33,13 +35,27 @@ int main(int argc, char *argv[])
 
 	while (running) {
 		tick_start = skele_time_ns();
+		skele_clock_tick_begin();
 
 		stk_poll();
 		game_tick();
+		skele_clock_tick_end();
+
+		if (tick_start - last_print >= 1000000000ULL) {
+			stk_log(STK_LOG_INFO,
+				"tps=%.1f tick=%lluns/%lluns idle=%lluns",
+				skele_tps,
+				(unsigned long long)skele_tick_time_ns,
+				(unsigned long long)skele_tick_ns,
+				(unsigned long long)skele_tick_idle_ns);
+			last_print = tick_start;
+		}
 
 		elapsed = skele_time_ns() - tick_start;
+		skele_clock_idle_begin();
 		if (elapsed < skele_tick_ns)
 			skele_sleep_ns(skele_tick_ns - elapsed);
+		skele_clock_idle_end();
 	}
 
 	game_shutdown();