Add a new primitive `string_indexOf_with_startIndex` that accepts a second integer argument to specify the starting position for the search. Modify the existing `wrenStringFind` function to accept a `startIndex` parameter, updating its Boyer-Moore-Horspool algorithm to begin scanning from the given offset. Update the `string_contains` primitive to pass `0` as the start index. Register the new overloaded method as `indexOf(_,_)` on the string class and add test cases covering boundary conditions and out-of-range start indices.
- 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
The benchmark directory is relocated from the project root into the test directory, and all scripts, documentation links, and gitignore paths are updated accordingly. The test runner is also refactored to explicitly walk subdirectories (core, io, language, limit) instead of using a single test root, and a new test/README.md is added to document the test suite structure. Additionally, the constructor test for the Foo class is updated to add a zero-arity constructor and adjust expected output strings.
