Fix time_ns() freeze rounding error

The previous behavior of time_ns() mock did round the value of the
frozen date to the seconds, excluding the microseconds if specified

This is mostly problematic when freeze_time() is used with the uuid1()
method: multiple "frozen" dates within the same second would all
generate the same uuid

freezegun/api.py

@@ -183,7 +183,7 @@ def fake_time():
     def fake_time_ns():
         if _should_use_real_time():
             return real_time_ns()
-        return int(int(fake_time()) * 1e9)
+        return int(fake_time() * 1e9)
 
 
 def fake_localtime(t=None):

tests/test_datetimes.py

@@ -759,14 +759,25 @@ def test_time_ns():
     utc_time = local_time - datetime.timedelta(seconds=time.timezone)
     expected_timestamp = time.mktime(utc_time.timetuple())
 
-    freezer.start()
-    assert time.time() == expected_timestamp
-    assert time.time_ns() == expected_timestamp * 1e9
-    freezer.stop()
+    with freezer:
+        assert time.time() == expected_timestamp
+        assert time.time_ns() == expected_timestamp * 1e9
+
     assert time.time() != expected_timestamp
     assert time.time_ns() != expected_timestamp * 1e9
 
 
+@pytest.mark.skipif(not HAS_TIME_NS,
+                    reason="time.time_ns is present only on 3.7 and above")
+def test_time_ns_with_microseconds():
+    freezer = freeze_time("2024-03-20 18:21:10.12345")
+
+    with freezer:
+        assert time.time_ns() == 1710958870123450112
+
+    assert time.time_ns() != 1710958870123450112
+
+
 def test_compare_datetime_and_time_with_timezone(monkeypatch):
     """
     Compare the result of datetime.datetime.now() and time.time() in a non-UTC timezone. These