feat(types): modify types to use native u128 where possible

Proposed Changes

Modify types to use native u128 instead of ruint U128 for local (not onchain) versions of user operations.
Impacts gas limit and fee fields
Convert to U128/U256 when necessary
For EP v0.7 the only fallible conversion is for preVerificationGas which onchain can be a U256. It is assumed there are no use cases where PVG needs to be > u128. We we're already relying on a U256 -> u128 conversion for gas limit calculation anyway.
For EP v0.6 all the gas and fee fields can have a fallible conversion. It is also assumed there are no legitimate use cases where these values can be larger than u128. For gas/fee representations this would be larger than a block's gas limit or larger than the total amount of token supply for ETH.