Explicitly support Dart 3 and follow modern standards

[parlough]

• Expand SDK constraint to explicitly indicate support for Dart 3
• Replace colons for specifying optional named parameter default values with equal signs. Support for the using colons has been deprecated for a while and is no longer supported with a language version >= 3.
• Remove explicitly named library declaration which isn't used for anything.
• Adjust code generator to be compliant with dart format.
• Remove the author field in the pubspec which is deprecated and no longer used.