feat(auditor): dump fetched spends to local disk

[maqi]

This pull request primarily introduces changes to the SpendDagDb implementation in the sn_auditor package, specifically in the dag_db.rs and main.rs files. The changes aim to enhance the process of updating the Directed Acyclic Graph (DAG) from the network by storing spends (transactions) on disk for better tracking and auditing. This is achieved by adding a storage_dir parameter to the continuous_background_update method and modifying how spends are processed.

The most important changes are:

• sn_auditor/src/dag_db.rs: The continuous_background_update method in the SpendDagDb implementation now takes an additional storage_dir: PathBuf parameter. This directory path is used to store spends on disk.
• sn_auditor/src/dag_db.rs: The spend processing logic has been updated. Now, each spend is hashed and stored in a detected_spends set. If a spend is new (not already in the set), it's written to a file in the storage_dir. The file name is a combination of the spend's address and hash.
• sn_auditor/src/main.rs: The main function now creates a storage_dir and passes it to the initialize_background_spend_dag_collection function.
• sn_auditor/src/main.rs: The initialize_background_spend_dag_collection function now takes an additional storage_dir: PathBuf parameter. This is passed to the continuous_background_update method of the SpendDagDb instance. [1] [2]

These changes are important as they help in tracking and auditing transactions by storing them on disk. This makes it easier to inspect individual transactions and provides a persistent record of transactions for auditing purposes.

[maqi]

Replaced by the PR #1973