Convert the arithmetic tests to pure Alan

[dfellis]

Not converting everything yet because:

1. Maybe there's a mistake that requires a refactor. This PR is already large enough as it is if that's the case.
2. I don't have a good story for doing the GPGPU tests, so I can't convert those yet, and those are the tests I ran into.
3. I'm curious how much just this saves. :)

[dfellis]

Even just this small amount has drastically improved things.

From this:

To this:

That's a 48% reduction in runtime for Linux, 44% for Windows, 31% for MacOS, and 35% for ARM Linux. And that's only removing the arithmetic tests from the Rust test suite to the new Alan test suite (I will note that it was a kludge that was also intended to end-to-end test the compiler, but still).

That did reduce the number of tests in the Rust CI from 250 to 139, which is a 44.4% decrease on that side, implying that for my Linux desktop the testing bottleneck is almost 100% due to compilation time, while for my older hardware (the 2014 Mac mini and the Raspberry Pi) there is some impact from actually running the tests, as well.