[CI] Migrate to cargo-llvm-cov

[patrick-ogrady]

cargo-tarpaulin incorrectly attributes coverage in a number of different cases: xd009642/tarpaulin#351

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.16%. Comparing base (6d499d6) to head (22e5641).

@@             Coverage Diff             @@
##             main     #110       +/-   ##
===========================================
+ Coverage   81.13%   92.16%   +11.03%     
===========================================
  Files          36       45        +9     
  Lines        2688     7125     +4437     
===========================================
+ Hits         2181     6567     +4386     
- Misses        507      558       +51     

Files with missing lines	Coverage Δ
p2p/src/simulated/mod.rs	98.79% <100.00%> (ø)

... and 44 files with indirect coverage changes

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