Modify optional workflows to be triggered by comments

[loicdiridollou]

• Closes Create a way to test nightly locally, or as part of a PR that fixes nightly #613 (Replace xxxx with the Github issue number)
• Tests added: Please use assert_type() to assert the type of any return value

This PR tries to modify how we run nightly/strict workflows to avoid having to run them systematically on merge to main but instead by able to do so by commenting on the PR with comments like /pandas_nightly, mypy_nightly or /pyright_strict.

The process would go as such:

• You write some code and open a PR in the repo
• You comment in the PR one of the commands like /pandas_nightly as below

- From there, the action kicks in and run the tests. - Once done, the results are published in a check run like below with a link to the action so that it is convenient to access the detailed results.

[loicdiridollou]

Right now there is a bit of code duplication in the yaml file but open to clean up, I will add a readme file to guide the operations.

[Dr-Irv]

I'm going to let @twoertwein review, approve and merge this, but one thing that I see is that you removed the optional runs that occur during a merge. I think those should remain, because otherwise, as someone doing many of the merges and getting those reports, I won't see what's failing on a regular basis and know what needs to be fixed.

[loicdiridollou]

I'm going to let @twoertwein review, approve and merge this, but one thing that I see is that you removed the optional runs that occur during a merge. I think those should remain, because otherwise, as someone doing many of the merges and getting those reports, I won't see what's failing on a regular basis and know what needs to be fixed.

I misunderstood then, I thought the idea was to replace as those optionals were put in place as a workaround. I will restore them so that they get triggered at every merge, sorry for that.

[Dr-Irv]

Thanks @loicdiridollou