Refactor writeContract and sendTransaction

[alvrs]

• we don't need writeContract anymore since it uses sendTransaction internally. All our custom logic can go into sendTransaction
• use an action for estimateFeesPerGas that caches the latest value and polls to refresh in the background instead of FeeRef
• use getAction(client, sendTransaction, "sendTransaction") instead of viem_sendTransaction
• if a nonce is passed in as a parameter, we should prioritise it
• add the block tag for nonce manager as an option
• allow configuring repricing logic for replacing txs with overlapping nonces (i.e. latest block tag for nonce then nonce gets reset but there's already txs in the mempool)
  • change nonce manager to fetch transaction count from "latest" instead of "pending" #2676