- Delete wren_io.c, wren_io.h, and io.wren source files
- Remove multi-arity print overloads and IO.read/IO.time methods
- Add System class with print, printAll, write, writeAll methods to core.wren
- Update all documentation examples and README to use System.print instead of IO.print
Add a generic `contains` implementation on the `Sequence` base class, removing the duplicate method from `List`. This allows all sequence types (including Range) to use the method without per-class redefinition. Include new test files for `List.contains` and `Range.contains` covering ordered, backwards, and exclusive ranges.
