tests: Add more serialise tests
tests: Add more serialise tests

While working the 32bit support (in the `wip/32bit` branch), I
figured it would be best to include tests for explicit 64 bit
values, so they could be regression tested on 32 bit systems.

This helped me find some other bugs, so, it seems like it was
a good idea.

Signed-off-by: Austin Seipp <7ea35d812706d9213868749011af1ed4fa2f6aa0@well-typed.com>

arianvp/binary-serialise-cbor,arianvp/binary-serialise-cbor