Include other-code source-ref in some compiler error messages

[nachumg]

Implements #231

[nachumg]

Hi, why does it fail:

1. python 3.5 - https://github.com/SystemRDL/systemrdl-compiler/actions/runs/12098641358/job/33735331485?pr=235 - what did I break?

2. mypy - I didn't change those files that it is complaining about - do you want me to fix those in a separate change?

[coveralls]

coverage: 94.653% (-0.2%) from 94.826%
when pulling 817f5ff on nachumg:main
into 649519b on SystemRDL:main.

[amykyta3]

Not quite. the ref variable you are using is not the same as src_ref.
Either way, I have implemented this in a separate commit and will close this PR.