Retrieve account details in parallel

Right now, when retrieving the account details, e.g. balance, rewards, delegated each one of this is a blocking call to the REST API. In the future, leverage Go concurrency capability to retrieve the account details in parallel to improve user experience and speed.

Start by locating the account-details retrieval entry point and the REST calls for balance, rewards, and delegated data. Confirm how these calls currently block one another; done means the three details are retrieved concurrently while preserving the account-details result and error behavior.

Written by the indexing model from the issue text.