Better Float / Decimal Type Management in Cache

[StuartFarmer]

Data is encoded to and from floating points deterministically if pulled from RocksDB. However, floats and decimals retain their Python object equivalent if they are in the cache.

Currently, there is a small shim that just checks if an object is a Decimal and casts it to a ContractingDecimal that is restricted and deterministic. This might not be the best way to do things.

Discuss alternatives later...