Implement module loader with top-level await support

[CNSeniorious000]

Implement a module loader that supports top-level await expressions. Many console environments (PyodideConsole, IPython, asyncio.__main__, trio.__main__, etc.) already allow direct await at module level, so supporting this in our module loader would enable loading async modules properly in interactive environments.

[linear]

PROM-72 Implement module loader with top-level await support

[CNSeniorious000]

All use ast.PyCF_ALLOW_TOP_LEVEL_AWAIT flag — standard approach since Python 3.8.