gh-140287: Handle PYTHONSTARTUP script exceptions in the asyncio REPL

[johnslavik]

This is generally a work in progress; tests are needed.
The asyncio patch is simple and ready.

• Issue: The asyncio REPL interactive daemon thread doesn't handle PYTHONSTARTUP exceptions #140287

[johnslavik]

Please merge #140298 first.

[johnslavik]

Looks like I was confused about the regression -- that's good news!

This will have to wait until the loop is properly closed in the asyncio REPL.

[johnslavik]

Cherry-picked 92f629b (875fd2a) from GH-142785 to see if it fixes the problem.

[johnslavik]

to see if it fixes the problem.

It does! Cool!

[johnslavik]

I really don't like this, but it resembles the original behavior of the REPLs -- see GH-143023.
I don't think this is correct, but it's not super clear to me, so please chime in to GH-143023 to put your two cents in.

Suggested change

	except SystemExit:
	raise
	# TODO: Revisit in GH-143023
	except SystemExit:
	raise

[johnslavik]

GH-143023 is also why I didn't add a test for this.

[johnslavik]

We've got some good news, this is not bad! I'll add a test shortly.

[johnslavik]

I'll see if I can simplify this. I think the tests are slightly overcomplicated.

[johnslavik]

I'll come back to this after completing GH-140648.

[johnslavik]

I've realized that this isn't testing what it is supposed to test. I'll come back to this later.