Support currencies in openleadr-wire (#54)

[joshuathayer]

Hi! This addresses #54.

In the issue it's left open whether to add currency support via a crate or by manually maintaining the list of current currencies listed here. The iso_currency crate seems popular (65k recent downloads) and maintained (last updated three months ago), and easy enough to integrate, so I opted to use it. I'd be happy to copy/paste the enum from that crate if you'd rather maintain it manually.

Also added a couple simple tests demonstrating serde for the currency field in EventPayloadDesciptor.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.50%. Comparing base (aa74877) to head (6fef8e6).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   81.40%   81.50%   +0.10%     
==========================================
  Files          42       42              
  Lines        5495     5521      +26     
==========================================
+ Hits         4473     4500      +27     
+ Misses       1022     1021       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[pohlm01]

Thanks a lot for your PR. I think the crate you are proposing looks nice and even if maintaining our own list is not a lot of work, we would most likely miss relevant updates to currencies in the world that Dependabot can provide to us though this crate.
In addition to the minor comment I left in the code, please make sure Clippy is also happy. Other than that, your code looks good to me.
Let me know if you have any further questions, either related to this PR or other issues you might want to contribute to.

[joshuathayer]

@pohlm01 thanks for the review. I've fixed up those changes, take a look when you can!

It seems like #53 might be a good next issue, though I suspect I'll have a couple questions.