codecov incorrectly treats rust and python separately

[rsyi]

As-is, codecov is treating the rust and python libraries separately, meaning code coverage is calculated only from the latest file that is uploaded to codecov, rather than merging the two codecov files and treating them as two parts of a whole.

See https://docs.codecov.io/docs/merging-reports for more information about how to do this correctly

Need to modify our github actions accordingly