fix tarpaulin code coverage and add .vscode to gitignore

[jonZlotnik]

the github action for tarpauling breaks often, and it's not worth depending on it when it's just as easy (and more transparent) to run it using the cargo action

evidence of frequent breakage:
actions-rs/tarpaulin#15
actions-rs/tarpaulin#23

[codecov]

Codecov Report

Patch coverage: 72.64% and project coverage change: +0.08 🎉

Comparison is base (5778854) 43.18% compared to head (a82a7ae) 43.27%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
+ Coverage   43.18%   43.27%   +0.08%     
==========================================
  Files          17       18       +1     
  Lines        2554     2542      -12     
==========================================
- Hits         1103     1100       -3     
+ Misses       1451     1442       -9     

Impacted Files	Coverage Δ
src/forwarding.rs	0.00% <0.00%> (ø)
src/transit/crypto.rs	43.26% <12.00%> (-6.08%)	⬇️
src/transfer/v1.rs	34.34% <50.00%> (-0.44%)	⬇️
src/transfer.rs	40.20% <75.00%> (-1.10%)	⬇️
src/util.rs	37.25% <80.00%> (+1.83%)	⬆️
src/transit.rs	75.24% <80.59%> (-0.86%)	⬇️
src/transit/transport.rs	84.53% <84.53%> (ø)
src/core/rendezvous.rs	74.01% <100.00%> (+0.98%)	⬆️
src/transfer/messages.rs	55.55% <0.00%> (-3.07%)	⬇️
... and 7 more

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[piegamesde]

Thank you. One minor thing: please split out the gitignore change into a separate commit.