add failing test

[omarandlorraine]

This is connected to issue #45, which is really about what happens in decimal mode if we're working with bytes that are not valid BCD.

So this commit adds a failing test, which is basically the output from Visual6502 after running the short program in the Issue I filed.

[mre]

With #47 being merged, I guess we can tackle this one again. Tried to rebase it, but it's currently failing. Do you think we should make the test pass or shall we close the PR? 🤔

[omarandlorraine]

Do you think we should make the test pass or shall we close the PR?

I think the test should pass. But on the other hand, with solid65 on the way, there will be more tests to come. This will look at decimal mode much more stringently as well and maybe find more bugs I haven't.

Tried to rebase it, but

I've gone and rebased it in case we want to proceed with it