Create a generic RsaPublicKey class that serves as a wrapper around RSA public key material in OpenSSL. Aside from the key material, it should also store a unique_ptr to the EVP_PKEY representation of the public key so that it can be used with the AsymmetricKeySignatureVerifier.

Write a unit test to verify that the class can be created and properly converts Base64EncodedURL keys into byte arrays in the class.

More details are available in the design document here.