eth/fetcher: fix blob transaction propagation

[roberto-bayardo]

This PR fixes an issue with blob transaction propagation due to the blob transation txpool rejecting transactions with gapped nonces. The specific changes are:

• fetch transactions from a peer in the order they were announced to minimize nonce-gaps (which cause blob txs to be rejected

• don't wait on fetching blob transactions after announcement is received, since they are not broadcast

Testing:

• unit tests updated to reflect that fetch order should always match tx announcement order
• unit test added to confirm blob transactions are scheduled immediately for fetching
• running the PR on an eth mainnet full node without incident so far