feat: improve logger in Serinus to be more robust and consistent

[francescovallone]

What is your proposal

The logger in Serinus is informative but can be more informative, easy to use and testable. The idea is to convert the "onLog" function to a proper class called "Printer" so that it is easier to extend Logger capabilities. Also the logger should allow the user to choose an output.

[francescovallone]

This is a comparison between the old and the new interface of the LoggerService:

Old

LoggerService({
    LogCallback? onLog,
    LogLevel level = LogLevel.debug,
    String prefix = 'Serinus',
})

New

LoggerService({
    Printer printer = DefaultPrinter(),
    Output output = DefaultOutput()
    LogLevel level = LogLevel.debug,
    String prefix = 'Serinus',
})

[francescovallone]

The Output field is not needed and can be merged inside the Printer