handle parity_ vs get_block_receipts in ParityMiddleware

[univerz]

this commit in ethers-rs unified parity_block_receipts & get_block_receipts with a good intention, but as a sad consequence, it was no longer possible to query offline db (== rpcdaemon without erigon running all the time) as it requires runtime client check & change was reverted.

it looks like it's possible to handle this better in this experimental middleware :).

[prestwich]

status: the work in ethers-rs has been backported here