New AddressState module to integrate balance deltas

[sandtreader]

Create a new AddressState module which subscribes to AddressDeltas (see #4 ) and integrates them into in-memory (for now) address balances. The module should be able to handle payment addresses, staking addresses, or both (we assume they are disjoint hash sets).

On a change, it should optionally issue an AddressBalance update - grouped by block for efficiency.

Note that addresses can hold multiple asset classes.

It should optionally provide a REST query to obtain the balance of a given address.

[sandtreader]

No longer a requirement to track staking addresses (AccountsState does this), and payment address balances are not needed for SPDD - however being able to query them is a use case in itself. This could be folded into AccountState, or a new module, which could be configured to handle either payment or staking or both, enabling it to be used for simple address queries even if AccountState isn't present.

[sandtreader]

It could also (as an option) remember the contributing UTXOs and provide an address->UTXO lookup REST endpoint

[sandtreader]

BlockFrost provides the following

/addresses/{address}
/addresses/{address}/extended
/addresses/{address}/total
/addresses/{address}/utxos
/addresses/{address}/utxos/{asset}
/addresses/{address}/txs
/addresses/{address}/transactions

This module should be able to provide these