Add automatic env reuse for py_event_loop:run

[benoitc]

Summary

• Functions defined via py:exec(Ctx, Code) can now be called via py_event_loop:run without manual env passing
• The process-local env is automatically detected and passed to the NIF
• Supports both sync and async functions defined in the process namespace

Example:

Ctx = py:context(1),
ok = py:exec(Ctx, <<"
async def async_add(a, b):
    await asyncio.sleep(0.01)
    return a + b
">>),

%% Just works - env is reused automatically
{ok, 42} = py_event_loop:run('__main__', async_add, [10, 32]).