delays in coroutines make gpmc detect unfinished threads deadlock

[dmitrii-artuhov]

GPMC incorrectly handles the delay's in the coroutine bodies.
Relates to #390

Problem

MInimal reproducing test:

@OptIn(ExperimentalModelCheckingAPI::class)
    @Test
    fun test() {
        runConcurrentTest(1000) {
            val pool = Executors.newFixedThreadPool(2).asCoroutineDispatcher()
            pool.use {
                runBlocking(pool) {
                    val nElements = 2
                    val channel = Channel<Int>() // RENDEZVOUS

                    launch(pool) {
                        for (i in 1..nElements) {
                            channel.send(i)
                            delay(1 /* ms */)
                        }
                        channel.close()
                    }

                    for (i in 1..nElements) {
                        val element = channel.receive()
                        check(element == i)
                    }
                }
            }
        }
    }

GPMC reports:

...
All unfinished threads are in deadlock

Expected

• Execution should not hang
• ?? delay's should be no-op ??