examples/usercmodule: Add example of a native C class.

This shows how ports can add their own custom types/classes.

It is part of the unix coverage build, so we can use it for tests too.

Signed-off-by: Laurens Valk <laurens@pybricks.com>

tests/misc/cexample_class.py

@@ -0,0 +1,20 @@
+# test custom native class
+
+try:
+    import cexample
+    import time
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+t = cexample.Timer()
+
+print(t)
+print(t.time() <= 1)
+
+time.sleep_ms(100)
+
+elapsed = t.time()
+
+if not (99 <= elapsed <= 110):
+    print("Elapsed time should be approx. 100ms but it is", elapsed)