feat: Added lang to frame and stacktrace

[mitsuhiko]

This adds a lang attribute to frame and stacktrace which is going to be used
to permit language specific handling.

[codecov-io]

Codecov Report

Merging #186 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #186      +/-   ##
==========================================
+ Coverage   64.68%   64.69%   +<.01%     
==========================================
  Files          83       83              
  Lines        9004     9006       +2     
==========================================
+ Hits         5824     5826       +2     
  Misses       3180     3180

Impacted Files	Coverage Δ
general/src/protocol/stacktrace.rs	96.72% <100%> (+0.05%)	⬆️

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[jan-auer]

WFM, although it would be good to get "standard" names for our known languages typed out in an enum. Should also align with Language in symbolic. Could be an enum with an Other variant then.

[mitsuhiko]

I was considering this but for now i only want that mapping in Python.