cicd: use cargo tools code coverage

[cboudereau]

• [x] add xtask
• [x] setup vscode + cicd code coverage with grcov and xtask coverage
• [x] update git workflow

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +2.21% :tada:

Comparison is base (b9a8baf) 84.89% compared to head (fe20a60) 87.11%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #25 +/- ## ========================================== + Coverage 84.89% 87.11% +2.21% ========================================== Files 14 14 Lines 1251 2056 +805 ========================================== + Hits 1062 1791 +729 - Misses 189 265 +76 ``` | [Files Changed](https://app.codecov.io/gh/cboudereau/gcs-rsync/pull/25?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Cl%C3%A9ment+Boudereau) | Coverage Δ | | |---|---|---| | [tests/objects\_integration\_test.rs](https://app.codecov.io/gh/cboudereau/gcs-rsync/pull/25?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Cl%C3%A9ment+Boudereau#diff-dGVzdHMvb2JqZWN0c19pbnRlZ3JhdGlvbl90ZXN0LnJz) | `95.52% <100.00%> (-3.34%)` | :arrow_down: | ... and [13 files with indirect coverage changes](https://app.codecov.io/gh/cboudereau/gcs-rsync/pull/25/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Cl%C3%A9ment+Boudereau)

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