refactor: Switch stake address state from Mutex<HashMap> to DashMap

[whankinsiv]

The stake_addresses field in accounts_state was previously using a Mutex<HashMap> to store stake address state. As the new StateQuery message type is adopted, read access to stake_addresses is becoming increasingly frequent, a trend that will continue as additional cross-module queries are implemented.

This PR refactors stake_addresses to use DashMap instead of Mutex<HashMap>, enabling fine-grained locking for writes and allowing fully concurrent reads. This significantly reduces contention under load, such as when syncing to tip.

I had observed that some StateQuery messages from drep_state to accounts_state were timing out. After switching to DashMap, these timeouts were resolved.

[whankinsiv]

The switch from Mutex<HashMap> to Dashmap may no longer be required as we are considering using historical states exclusively for StateQuery responses. This would make switching the live state unnecessary for the initial purposes of this PR. Any needed data structure changes will be included in the accounts_state refactor for expanding state to align with data required for Blockfrost. Closing this PR.