chore(ci): switch to cargo-llvm-cov for code coverage

[orhun]

Description

Switching to cargo-llvm-cov due to the recent bugs with cargo-tarpaulin.

How Has This Been Tested?

CI

Types of Changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (no code change)
• [ ] Refactor (refactoring production code)
• [x] Other: CI

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have formatted the code with rustfmt.
• [x] I checked the lints with clippy.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.11%. Comparing base (fa5105d) to head (7f84c70).

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #260 +/- ## =========================================== + Coverage 70.09% 82.11% +12.02% =========================================== Files 11 11 Lines 632 1219 +587 =========================================== + Hits 443 1001 +558 - Misses 189 218 +29 ``` | [Flag](https://app.codecov.io/gh/orhun/rustypaste/pull/260/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z) | Coverage Δ | | |---|---|---| | [unit-tests](https://app.codecov.io/gh/orhun/rustypaste/pull/260/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z) | `82.11% <ø> (+12.02%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z#carryforward-flags-in-the-pull-request-comment) to find out more.

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