Improve Dart sudoku

The Dart sudoku solution is a bit slow and has some simple fixes to improve performance.  Using the typedata Lists (Uint16List for example), can do a decent job increasing the speed of the app.  Also, don't use any growable lists (List.add is slow, much list ArrayList.add is slow in Java).

Formatting got screwed up a bit I think (I was using the Dart editor to make the changes, looks like whitespace changes on the file).