tests/thread: Add a test for accuracy of sleep within a thread.

The existing thread_sleep1.py test only tests execution, not accuracy, of
time.sleep.  Also the existing test only tests sleep(0) on targets like rp2
that can only create a single thread.

The new test in this commit checks for timing accuracy on the main thread
and one other thread when they run at the same time.

Signed-off-by: Damien George <damien@micropython.org>

tests/thread/thread_sleep2.py

@@ -0,0 +1,31 @@
+# Test accuracy of sleep within a thread.
+
+import time
+import _thread
+
+
+def sleep(t, valid_range):
+    t0 = time.time_ns()
+    time.sleep(t)
+    dt_ms = (time.time_ns() - t0) // 1_000_000
+    if dt_ms in valid_range:
+        print("dt in range", t)
+    else:
+        print("dt not in range:", dt_ms)
+
+
+def thread_entry():
+    lock.acquire()
+    print("thread start")
+    sleep(0.2, range(180, 400))
+    print("thread end")
+
+
+lock = _thread.allocate_lock()
+lock.acquire()
+_thread.start_new_thread(thread_entry, ())
+
+print("main start")
+lock.release()
+sleep(0.5, range(480, 800))
+print("main end")