Refactor Logger

[stevenzeck]

Refactored Logger to be Swift 6 compliant.

Public API Breaking Changes

1. Logger is now an actor: Any external code that directly interacts with Logger.sharedInstance (such as calling setupLogger or setMinimumSeverityLevel) must now do so asynchronously using await from an asynchronous context or inside a Task.
2. LoggerType.log signature changed: The value parameter type was changed from Any? to String?.
   • Old: func log(level: SeverityLevel, value: Any?, file: String, line: Int)
   • New: func log(level: SeverityLevel, value: String?, file: String, line: Int)
3. Asynchronous Logging Behavior: While the method signatures of the Loggable extension (log, warnIfMainThread, etc.) and the ReadiumEnableLog() function remain the same, they now wrap their internal calls to the Logger actor in a Task. This means logging operations and logger setup are now fire-and-forget (asynchronous) rather than synchronous.

Related to #758.