[98] Prepare retained logs for deferred processing

[filipovskid]

Description of changes

Resolves #98.

• Resets the logger context to remove existing appenders.
  • Currently, the ROOT logger has a ConsoleAppender attached, which introduces side effects that can interfere with testing the RetainingAppender.
• Prepares retained logs for deferred processing as documented in [LoggingEvent.html#prepareForDeferredProcessing()](https://logback.qos.ch/apidocs/ch.qos.logback.classic/ch/qos/logback/classic/spi/LoggingEvent.html#prepareForDeferredProcessing())