Vendor debugpy for VS Code attach debugging

Bundles debugpy 1.7.0 directly in python/ so "Maya: Attach (debugpy)"
works with no per-machine pip install step. Installed via Maya 2022's
own pip so it resolved a version actually compatible with Python 3.7
(Maya 2022's interpreter), then verified import + listen() succeeds
under all three target Maya Python versions (3.7/3.9/3.10).

Also fixes a latent __file__-under-exec() bug in
start_debug_server.py (same pitfall as Maya's own plugin loader,
never hit until this exercised it) and corrects the README's Maya
Python version claim -- 2022 ships Python 3.7, not 3.9 as previously
stated, which was never independently verified until now.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python/debugpy/_vendored/pydevd/tests_mainloop/gui-pyglet.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+"""Simple pyglet example to manually test event loop integration.
+
+To run this:
+1) Enable the PyDev GUI event loop integration for pyglet
+2) do an execfile on this script
+3) ensure you have a working GUI simultaneously with an
+   interactive console
+"""
+
+if __name__ == '__main__':
+    import pyglet
+    
+    
+    window = pyglet.window.Window()
+    label = pyglet.text.Label('Hello, world',
+                              font_name='Times New Roman',
+                              font_size=36,
+                              x=window.width//2, y=window.height//2,
+                              anchor_x='center', anchor_y='center')
+    @window.event
+    def on_close():
+        window.close()
+    
+    @window.event
+    def on_draw():
+        window.clear()
+        label.draw()