Remove the automatic fflush(stdout) call from the write() function in vm.c, which was causing gratuitous performance overhead on every System.write() invocation. Introduce a new Stdout class with a foreign static flush() method that delegates to fflush(stdout), giving users explicit control over when output is flushed. Update the io module registration in modules.c to include the Stdout class and bump MAX_CLASSES_PER_MODULE from 5 to 6. Add documentation for Stdout in doc/site/modules/io/stdout.markdown, update the io index and template to list the new class, and add flush() usage notes to the Stdin readByte() and readLine() docs. Implement the stdoutFlush() foreign function in io.c.
Implement asynchronous stat() on File class returning a new Stat object with device, inode, mode, linkCount, user, group, specialDevice, size, blockSize, and blockCount fields populated from libuv uv_fs_stat callback. Register foreign method statPath_ in module registry, bump MAX_METHODS_PER_CLASS to 10, add Stat class to io.wren with indexed field accessors, update documentation index with Stat page, and include test coverage for stat on existing file and nonexistent path.
Restructure the documentation hierarchy to prepare for documenting additional built-in modules. Move all core library documentation from `doc/site/core/` to `doc/site/modules/core/`, rename `modules.markdown` to `modularity.markdown`, remove `^category` metadata lines from all affected pages, update cross-reference links to use relative paths under the new structure, and add a TODO placeholder to the Class class page.
