feat(bindings): Add API to check for resumption

[goatgoose]

Resolved issues:

Resolves https://github.com/aws/s2n-tls/issues/4263

Description of changes:

Adds a new API to the rust bindings that corresponds to s2n_connection_is_session_resumed(), which determines whether the connection was resumed.

Call-outs:

I changed the API name to be past tense, since the handshake would have already occurred when this API is called. But let me know if you think is_resumed() would be better, or if there's another name that would be better.

Testing:

I updated the session resumption tests to use this API to check for resumption and the absence of resumption, and the tests succeed.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.