feat: add `id_from_pos` support

[LagginTimes]

This PR introduces the blockchain.transaction.id_from_pos feature from Electrum. This functionality is essential for an ongoing implementation in bdk_electrum, which requires retrieving the coinbase transaction from a block at a specified height. Currently, there is no straightforward method to achieve this. By implementing the id_from_pos feature, we will effectively address this gap.