Support assertions in `TestWorkflowEnvironment.registerDelayedCallback`

Is your feature request related to a problem? Please describe.

When assertions fail in TestWorkflowEnvironment.registerDelayedCallback, the errors in the callback are swallowed. This is counterintuitive.

For instance, I expect the following test to fail.

class MyTest {

  private val testEnv: TestWorkflowEnvironment
  
  @Test
  fun thisShouldFail() {
    testEnv.registerDelayedCallback(Duration.ofSeconds(1)) {
      assertThat(false).isTrue()
    }
    testEnv.sleep(Duration.ofSeconds(10))
  }
}

But it succeeds with an error log.

10:35:11.197 [Timer task] ERROR i.t.i.t.SelfAdvancingTimerImpl - Unexpected failure in timer callback
org.opentest4j.AssertionFailedError: 
Expecting value to be true but was false
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

Describe the solution you'd like
Propagate the error to the test method.

Start by locating TestWorkflowEnvironment.registerDelayedCallback and the timer callback handling it. Reproduce the Kotlin example, then trace how callback failures are reported; done means an assertion failure in the delayed callback causes the test method to fail rather than only producing an error log.