fle_crypto.h is included by expression.h which is included by ~1000 files either indirectly or directly. This means any incremental change to fle_crypto.h requires recompiling 1000 files.

We should split fle_crypto.h into three files
fle_crypto_types.h
fle_crypto_predicate.h
fle_crypto.h

The first two are needed by expression.h and can include code that less frequently changes instead of all of the FLE API.