Codecov troubleshooting tracker

[scorbajio]

Copied over from #3751:

• The master branch isn't having coverage pushed/calculated/visualized, so I'll see if this is just a misconfig or something (Further troubleshoot current codecov CI issues #3751)
• Some packages (devp2p, wallet, genesis, client) aren't having their coverage files uploaded? Or, atleast they're not showing up on codecov at the moment, so I'll triage and followup here. (devp2p, wallet, genesis are being fixed at Rework rlpx-simulator.spec.ts tests / Fix devp2p/genesis/wallet Coverage Reporting  #3760)
• As mentions by @jochem-brouwer, most of the coverage diffs seem to not be calculates/reported ( Troubleshoot codecov failures to upload coverage data #3376 (comment)).
• rlp and ethash packages are uploading coverage reports, but their reports are erroring out as unusable. I remember working on this before and opening a codecov ticket on it too (in the codecov official repo) that didn't get much activity, but will look into and followup on this on as well.