Handle critical errors

[idky137]

Adds automatic server restart for critical errors.

• propagates errors from child processes to Indexer.
• Updates Indexer::serve and Indexer::start to return IndexerErrors properly.
• Updates main to restart on Critical errors.

PR details:

• Build on top of Compact block cache pt3 #170, Add terminal log #177, Zaino-Serve 2.0 #180.
• Closes Task 2.2.3: Add automatic server restart / shutdown for critical errors. #128.

[idky137]

Helper fn merged, Current test failures in zaino_testutils, zaino_state::fetch and integration_tests::wallet_to_validator are fixed in #186.