Smoke test for built gem

[anakinj]

We have had a few issues in the past when the release version has not started properly because:

• Something being loaded via some dev/test dependencies made everything work on CI JWT::JWK::EC needs require 'forwardable' #392
• Something loaded differently for a built gem link

I think it would be valuable to have something on the CI that would build the current version and require the output and do some simple encoding and decoding.