Add expected test results

[micw]

Hello,

IMO it would make sense to add the expected results (e.g. a list of extracted obis codes, units and values) so that this can be used to create unit tests.

[felixwrt]

I'm not sure how the expected files should look like. I'd expect the format to heavily depend on the actual implementation and how detailed it parses the data.

In sml-rs, I tried to make the parser lossless in a sense that every attribute present in the SML spec can be accessed. I'm using debug outputs of the parsed data for my expected files. I went through them once to see whether the output makes sense. I'm using them to detect regressions now.

Here's my expected files, in case you are interested: https://github.com/felixwrt/sml-rs/tree/main/tests/snapshots

[devZer0]

that's something that we can think about, but i have no ressources for this at the moment. sorry