Replace or Upgrade Tarpaulin Code Coverage

[iamjpotts]

tarpaulin may be incompatible with newer versions of Node and cause CI failures.

#264 disables the code coverage step in CI.

I don't have a view as to what direction to take afterwards, but that probably depends on if/when tarpaulin #22 gets released.

[vmx]

Other options are:

• using tarpaulin directly: https://github.com/xd009642/tarpaulin#github-actions
• llvm-cov: https://github.com/taiki-e/cargo-llvm-cov#continuous-integration ,

[vmx]

This was fixed by #295.