Entity embedding layers should output Float32 not Float64, as present?

[ablaom]

While less generic, I'm inclined to agree with the proposal at #272, which is to coerce all data to Float32, with no option to opt out. So I suggest we also make Float32 the output type for the entity embedding layers. This does not appear to be the case at present, and this is complicating resolution of the conflict at #272: When data is not Float32 and is coerced to Float64, a warning is issued, but the warning is breaking certain tests (admittedly fragile) that depend on logging to check certain functionality (warm restarts).

cc @EssamWisam