Fix MicroPython badly handling unicode chars (#2018)

## Changes

  * fixed an issue with the **py-editor** related to the new `linebuffer` directive
  * provide in worker hook scope a simple callback that pre-buffers unicode sequences [accordingly to the standard](https://encoding.spec.whatwg.org/#utf-8-bytes-needed) so that the buffer is sent to the terminal only once those sequences are fulfilled
  * test with both `µ` and way more convoluted sequences such as 👩‍❤️‍👨 that the output, if either requested as input or already evaluated from the page works ... in latter case `test = "👩‍❤️‍👨"` completely messes up the program and the resulting string is empty

pyscript.core/src/plugins/py-editor.js

@@ -15,8 +15,8 @@ const hooks = {
         codeBeforeRun: () => stdlib,
         // works on both Pyodide and MicroPython
         onReady: ({ runAsync, io }, { sync }) => {
-            io.stdout = (line) => sync.write(line);
-            io.stderr = (line) => sync.writeErr(line);
+            io.stdout = io.buffered(sync.write);
+            io.stderr = io.buffered(sync.writeErr);
             sync.revoke();
             sync.runAsync = runAsync;
         },