Check for event loop and start new loop if necessary

[JeffersGlass]

With get_event_loop() no longer implicitly starting a new loop as of Python 3.14, any dev tool commands which start a serve will fail with a RuntimeError. If this occurs, start a new event loop before running the aiohttp app.

Fixes #45

[TomJGooding]

EDIT: Sorry, probably just ignore the below! After looking into aiohttp.web.run_app(), I see this also uses asyncio.new_event_loop() if none was passed, so I've probably just misunderstood.

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Is asyncio.new_event_loop() definitely the correct replacement here?

I confess I'm no expert on asyncio, but reading up on the changes I found this post:

It is not correct to simply replace asyncio.get_event_loop() with asyncio.new_event_loop() because there's a number of important teardown steps that asyncio.Runner performs. Making this change will appear to work, but will silently cause problems