DeterministicRandom() can use a boost::random::mt19937_64
to take a 64-bit seed and return 64-bit random values,
and this simplifies things because fdb always wants 64 bits.
Performance should be slightly better because the 32-bit
mt19937 was always called twice to get 64 bits.
* fix: use thread-local mt19937_64 for automatic idempotency ID
* feat: add platform::getRandomBytes and use it for idempotency IDs
* fix: pr fixes + getentropy support
* fix: pr review changes
Trevor Clinkenbeard