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.

src/module/io.c

@@ -4,28 +4,13 @@
 #include "uv.h"
 
 #include "scheduler.h"
+#include "stat.h"
 #include "vm.h"
 #include "wren.h"
 
 #include <stdio.h>
 #include <fcntl.h>
 
-// Windows doesn't define all of the Unix permission and mode flags by default,
-// so map them ourselves.
-#if defined(WIN32) || defined(WIN64)
-  #include <sys\stat.h>
-
-  // Map to Windows permission flags.
-  #define S_IRUSR _S_IREAD
-  #define S_IWUSR _S_IWRITE
-
-  #define S_ISREG(m) (((m) & S_IFMT) == S_IFREG)
-  #define S_ISDIR(m) (((m) & S_IFMT) == S_IFDIR)
-
-  // Not supported on Windows.
-  #define O_SYNC 0
-#endif
-
 typedef struct sFileRequestData
 {
   WrenHandle* fiber;