Fix BlockHeight and Maturity types

[AlicanC]

There is a confusion if these should be defined as u32s or u64s in the repo. The specs say it should be u32, but fuel-core GQL API uses U64s.

Either the spec or fuels-ts and fuel-core should be updated.

[adlerjohn]

There's an issue in the specs to make all those types u64 in favor of consensus rules to bound them rather than types. FuelLabs/fuel-specs#298

[Torres-ssf]

This Issue was already fixed