feat: add scroll to gas price oracle

[dohaki]

According to the last paragraph in https://docs.scroll.io/en/developers/transaction-fees-on-scroll/#l1-originated-transactions, we can use the legacy RPC call eth_gasPrice to determine the gas price on Scroll:

If your system supports off-chain mechanisms, you can also call eth_estimateGas and eth_gasPrice on any Scroll RPC node to get an estimate of the gas required for a given transaction.

Closes ACX-2356

[linear]

ACX-2356 sdk: Add Scroll gas price adapter

[pxrl]

How does this perform in test btw? Does it produce a gas price that kinda-resembles the onchain price advertised by Scrollscan?

According to the last paragraph in https://docs.scroll.io/en/developers/transaction-fees-on-scroll/#l1-originated-transactions, we can use the legacy RPC call eth_gasPrice to determine the gas price on Scroll:

If your system supports off-chain mechanisms, you can also call eth_estimateGas and eth_gasPrice on any Scroll RPC node to get an estimate of the gas required for a given transaction.

That's in the L1 Originated Transactions section, which I think is messaging from mainnet -> Scroll, so I'm, not sure whether it applies to our use case 🤔

In any case, it's probably sensible to just see how legacy pricing performs; if it's reasonably accurate (or over-estimates, but with an insignificant difference) then I think it's probably fine to proceed with that. If we need to go into more detail we can implement a Scroll-specific adapter that queries their gas oracle contracts.

[dohaki]

How does this perform in test btw? Does it produce a gas price that kinda-resembles the onchain price advertised by Scrollscan?
That's in the L1 Originated Transactions section, which I think is messaging from mainnet -> Scroll, so I'm, not sure whether it applies to our use case 🤔
In any case, it's probably sensible to just see how legacy pricing performs; if it's reasonably accurate (or over-estimates, but with an insignificant difference) then I think it's probably fine to proceed with that. If we need to go into more detail we can implement a Scroll-specific adapter that queries their gas oracle contracts.

Ah damn, yea you are right... It is less than the gas price displayed on Scrollscan. So yea I will re-work this PR and implement the adapter
EDIT: It looks like we should be able just to use eth_getGasPrice