CI Code Coverage Fix

[YJDoc2]

ref #226 #272
This attempts to Fix code coverage issue :
After seeing actions-rs/grcov#105, which asks to update code coverage using inbuilt features of llvm, as well as PyO3 also seems to use it, (which is quite a big lib). So I tried to use similar workflow as https://github.com/PyO3/pyo3/blob/main/.github/workflows/ci.yml to see if it can fix the issue.

[codecov-commenter]

Codecov Report

Merging #273 (a01be9d) into main (b8442af) will increase coverage by 28.70%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##             main     #273       +/-   ##
===========================================
+ Coverage   41.22%   69.92%   +28.70%     
===========================================
  Files          15       46       +31     
  Lines        1458     5693     +4235     
  Branches      412        0      -412     
===========================================
+ Hits          601     3981     +3380     
- Misses        645     1712     +1067     
+ Partials      212        0      -212     

[YJDoc2]

So I think this does work for accounting code coverage in cgroups as well. On codecov docs, it states that reports are merged : https://docs.codecov.com/docs/merging-reports So I think this merges the code coverage for youki as well as cgroups both.

On another node, this didn't spawn format and clippy jobs as no code was changed, which means the check job is working as expected !!! 🎉 🎉 🎉

@utam0k please take a look once, and verify.

[YJDoc2]

I also think the grcov.yaml file is not needed anymore and can be deleted, but not sure.

[YJDoc2]

Also, I just came around https://github.com/Swatinem/rust-cache, should we try changing our plain cache action with this one specifically for rust?

Update : I think we should take a look at https://matklad.github.io/2021/09/04/fast-rust-builds.html as well, seems really useful.

[utam0k]

Let's install it and measure the benchmarks!

Also, I just came around https://github.com/Swatinem/rust-cache, should we try changing our plain cache action with this one specifically for rust?