fixes #495: param and return types for eth_getStorageAt

[eshaan7]

Closes #495.

Changes

• Change slot param type to be U256 instead of B256.
• Change return value of eth_getStorageAt to be B256 instead of U256.

[ncitron]

I think it would probably be best to try and mirror the interface of alloy here, which is to make the keys and values both U256. By switching to U256 for the key this should resolve the issue, as U256 is not required to be padded to 32 bytes when deserialized.

As for the return type, alloy uses U256, but this does mean the rpc return type may not be padded with zeros and playing with alchemy it seems responses are usually padded, so maybe the B256 makes more sense, especially if the spec demands padding.

But definitely want to go from JsonStorageKey -> U256 at a minimum, as it is deserialized the same way (I think) and is the more commonly used type.

[eshaan7]

As for the return type, alloy uses U256, but this does mean the rpc return type may not be padded with zeros and playing with alchemy it seems responses are usually padded, so maybe the B256 makes more sense, especially if the spec demands padding.

Yes, I tried with both Geth and Reth and they are padding the return value so that's why I went with B256.

But definitely want to go from JsonStorageKey -> U256 at a minimum, as it is deserialized the same way (I think) and is the more commonly used type.

That makes sense. Will do a lil more manual testing to verify the deserialization is as expected.

[eshaan7]

@ncitron -- Made the slot param take U256. PTAL.

[ncitron]

LGTM!