Net::SSLeay assumes all libssl/libcrypto constants are doubles

[chrisnovakovic]

Raised by @h-vn in a comment in #313, but it deserves its own issue.

helper_script/regen_openssl_constants.pl (and, when #313 is merged, helper_script/update-exported-constants) generates C code that returns the values of libssl and libcrypto constants as doubles:

https://github.com/radiator-software/p5-net-ssleay/blob/4d9f7eaeeeb982ca3a92d469a0a6771d8031734c/constants.c#L3-L4

This assumes that the values of constants will never be greater than 2⁵³. This appears to be the case for all constants we currently export for all versions of OpenSSL and LibreSSL we currently support, although this isn't guaranteed to be true in future.