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/foreign/unknown_method.wren

@@ -1,3 +1,3 @@
 class Foo {
-  foreign someUnknownMethod // expect runtime error: Could not find foreign method 'someUnknownMethod' for class Foo in module 'test/language/foreign/unknown_method'.
+  foreign someUnknownMethod // expect runtime error: Could not find foreign method 'someUnknownMethod' for class Foo in module './test/language/foreign/unknown_method'.
 }