Replaces direct database queries for transactions with calls to the Fava API,
centralizing transaction logic and improving data consistency.
This change removes redundant code and simplifies the API by relying on Fava
for querying transactions based on account patterns and other criteria.
Specifically, the commit introduces new methods in the FavaClient class for
querying transactions, retrieving account transactions, and retrieving user
transactions. The API endpoints are updated to utilize these methods.
Implements an asynchronous HTTP client to interact with the Fava accounting API.
This client provides methods for adding journal entries, retrieving account balances,
and querying user balances, allowing the application to delegate all accounting
logic to Fava and Beancount.
