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/logical_short/logical_short.wren

@@ -0,0 +1,5 @@
+// Import a module whose name is the same as the package.
+import "foo" for Module
+// expect: ran module
+
+System.print(Module) // expect: from module

test/language/module/logical_short/wren_modules/foo/foo.wren

@@ -0,0 +1,3 @@
+// nontest
+var Module = "from module"
+System.print("ran module")