Add cargo-tarpaulin config file to ensure all features are ran

[rrybarczyk]

cargo tarpaulin is used to perform code coverage as a GitHub Action.

A cargo tarpaulin config file should be added that instructs the test to be executed with for the repo's feature flags: with-serde, with-noise, and prop-test. The config file will look something like this.

[rrybarczyk]

• PR #197 + #203 introduces the tarpaulin cmd in the .github/workflows/coverage.yaml GitHub Action and repeats the command in the README to be executed locally.
• Making a config file in the project root would still be helpful though

[pavlenex]

Done in #670