Add nonblocking jitter clock reads for video scheduling

src/call/call_jitter.cpp

@@ -226,6 +226,12 @@ void call_jitter_clock(struct call_jitter* j, int64_t now_us, struct call_clock_
     *out = j->timeline.clock(now_us);
 }
 
+int call_jitter_try_clock(struct call_jitter* j, int64_t now_us, struct call_clock_snapshot* out) {
+    std::unique_lock<std::mutex> lock(j->mtx, std::try_to_lock);
+    if (!lock.owns_lock()) return 0;
+    *out = j->timeline.clock(now_us); return 1;
+}
+
 void call_jitter_reset(struct call_jitter* j) {
     if (!j) return;
     std::lock_guard<std::mutex> lock(j->mtx);

src/call/call_jitter.h

@@ -46,6 +46,8 @@ void call_jitter_progress(struct call_jitter* j, uint64_t epoch, uint64_t positi
 void call_jitter_suspend_device(struct call_jitter* j, uint64_t epoch);
 /* Любой поток: снимок часов, включая epoch при valid=0. */
 void call_jitter_clock(struct call_jitter* j, int64_t now_us, struct call_clock_snapshot* out);
+/* Неблокирующее чтение: 1 — снимок получен, 0 — mutex занят. Аргументы должны быть валидны. */
+int call_jitter_try_clock(struct call_jitter* j, int64_t now_us, struct call_clock_snapshot* out);
 void call_jitter_get_stats(struct call_jitter* j, int* depth_ms, int* tempo_x100,
                            uint32_t* dropped, uint32_t* underruns, struct call_jitter_range* range);