feat: add logical import support with wren_modules directory resolution and path type classification

Introduce a path type classification system (absolute, relative, simple) to distinguish logical imports from relative ones. Implement automatic discovery of a "wren_modules" directory by walking up from the root directory. Refactor the CLI to return interpret results and exit codes instead of exiting directly. Extract cross-platform stat macros into a shared header. Update test API calls to use explicit relative paths.

test/language/module/compile_error/compile_error.wren

@@ -1,2 +1,2 @@
 System.print("before") // expect: before
-import "./module" for Module // expect runtime error: Could not compile module 'test/language/module/compile_error/module'.
+import "./module" for Module // expect runtime error: Could not compile module './test/language/module/compile_error/module'.