[Feature] Update Gas Price in Transaction Builder to use Type U256 instead of u128

[TheGreatAxios]

Component

network, json-rpc, rpc

Describe the feature you would like

The SKALE Network -> https://skale.space has a native gasless transaction feature.
The feature utilizes "magic numbers" to allow transactions to be sent without gas.
The value is set as gas price of a transaction.

However, the magic numbers are generally quite large (larger than u128) and result in an overflow.
If the value is updated to U256 the issue should be resolved.

Flagging as a feature since it's specific to SKALE Network.

Additional context

https://docs.skale.space/builders/tools/rng/

[mattsse]

sigh, that's terrible...

this would also mean we'd need to transition all types.
skpetical that we want to do this