feat(mempool): index mempool

[kodemon]

What would you like to be added:

Add mempool indexing to align with other explorers and pre-emptively update our own indexes to reflect better results for spendable and inscription transfers.

Why is this needed:

Currently we do minor tracking of movements that occur through our api. For example when someone relays a transaction we update our utxos with a spent state. Currently this only affects relays through our own api as we don't currently consume the mempool.

Another benefit is being able to handle known futures allows us to provide unconfirmed transaction information and show early movement of data such as BRC-20 and Sado events providing higher responsiveness of blockchain movement.