Fix pytest unstable issue. (#170)

- remove `#include <cstdint>` from `poll.hpp`. To make it only contains
device-side code
- Fix compilation issue, which will cause pytest fail randomly. Reuse
the compiled result for same kernel with different arguments

python/test/simple_proxy_channel_test.cu

@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
+#include "common.hpp"
+// other headers
 #include <mscclpp/packet.hpp>
 #include <mscclpp/proxy_channel_device.hpp>