test(time): Publish the TestTicker tick to other threads

The ANR tests advance the clock from the test thread while the watchdog
thread reads it, which without volatile is a data race that can leave the
watchdog looking at a stale tick forever.

Author: runningcode

sentry-test-support/src/main/kotlin/io/sentry/time/TestTicker.kt

@@ -9,11 +9,14 @@ import java.util.concurrent.TimeUnit
  * nanosecond clock is off by a factor of a million and still compiles, whereas `advance(1001,
  * MILLISECONDS)` cannot be.
  *
+ * The tick is volatile so that a test thread can advance the clock while the code under test reads
+ * it from another thread.
+ *
  * Implements both clock guarantees so a test can inject it wherever either is declared. Production
  * code must never do this — the whole purpose of the two interfaces is that one object cannot
  * honestly promise both.
  */
-class TestTicker(private var nanos: Long = 0) : UptimeClock, ElapsedRealtimeClock {
+class TestTicker(@Volatile private var nanos: Long = 0) : UptimeClock, ElapsedRealtimeClock {
   override fun tickNanos(): Long = nanos
 
   fun advance(amount: Long, unit: TimeUnit) {