Add --version argument to pgzrun (#355)

While developing on this project locally I wanted to check what version
of pgzrun I was using. That wasn't implemented so I added it to the
pgzrun runner.

It looks like this now:
```
$ pgzrun --version
pygame 2.6.1 (SDL 2.28.4, Python 3.13.2)
Hello from the pygame community. https://www.pygame.org/contribute.html
pgzrun 1.2.post5.dev202+gcd4f6dc.d20250413
```

Author: lordmauve

src/pgzero/runner.py

@@ -1,6 +1,7 @@
 from . import storage
 from . import clock
 from . import loaders
+from . import __version__
 from .game import PGZeroGame, DISPLAY_FLAGS
 from types import ModuleType
 from argparse import ArgumentParser
@@ -68,6 +69,11 @@ def main():
         action='store_true',
         help="Print periodic FPS measurements on the terminal."
     )
+    parser.add_argument(
+        '--version',
+        action='version',
+        version=f'%(prog)s {__version__}'
+    )
     parser.add_argument(
         'game',
         help="The Pygame Zero game to run (a Python file or directory)."