feat: add File.realPath() to resolve symlinks and normalize paths

Implement a new static method `File.realPath(path)` that resolves the given path by traversing symlinks and removing redundant `./` and `../` components, returning the canonical absolute path. The implementation uses libuv's `uv_fs_realpath` via an asynchronous callback pattern consistent with other File operations. Includes documentation, foreign method declarations, and two error-case tests for nonexistent paths and wrong argument types.

src/cli/modules.c

@@ -17,6 +17,7 @@ extern void fileSizePath(WrenVM* vm);
 extern void fileClose(WrenVM* vm);
 extern void fileDescriptor(WrenVM* vm);
 extern void fileReadBytes(WrenVM* vm);
+extern void fileRealPath(WrenVM* vm);
 extern void fileSize(WrenVM* vm);
 extern void fileStat(WrenVM* vm);
 extern void fileWriteBytes(WrenVM* vm);
@@ -115,6 +116,7 @@ static ModuleRegistry modules[] =
       FINALIZER(fileFinalize)
       STATIC_METHOD("delete_(_,_)", fileDelete)
       STATIC_METHOD("open_(_,_,_)", fileOpen)
+      STATIC_METHOD("realPath_(_,_)", fileRealPath)
       STATIC_METHOD("sizePath_(_,_)", fileSizePath)
       METHOD("close_(_)", fileClose)
       METHOD("descriptor", fileDescriptor)