new atime ci, no more old cml container

[tdhock]

The old atime CI uses an old container (old compilers etc.)
I propose switching to this new CI which is definitely more code.
Plus: easier to customize.
Minus: more maintenance burden.

[github-actions]

• HEAD=new-atime-ci much slower for isoweek improved in #7144
• HEAD=new-atime-ci slower P<0.001 for fwrite refactored in #6393
  

Generated via commit 4dc8c82

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	1 minutes and 5 seconds
Installing different package versions	16 minutes and 54 seconds
Running and plotting the test cases	5 minutes and 15 seconds

[MichaelChirico]

IIUC this is designed to supplant the old action which can't be updated? Is there anything stopping us from forking it instead (or, if the current PR is intended as such a fork, could we at least host it in a dedicated repo under Rdatatable or maybe under your tdhock?)

[tdhock]

right, the current PR is a fork. @Anirban166 would you consider putting this new code in your Autocomment-atime-results repo? (I was not sure if Ani is willing / able to continue maintenance, but that would be great)
The basic problem with the old action is that is uses an old cml container, old compilers, and this PR fixes that.