null instance action

[Ben-cpy]

null instance validation action, including some null instance combinations.

this is a basic version, random generate port would be used soon.

[haosanzi]

Please merge the two commits in the red box into the first commit. You only need to submit two commits, one to add null instance runtime tests and one to modify the path.

[haosanzi]

If you have solved the problem, please click the resolve conversion button.

[imlk0]

@cheatguy LGTM.

Also, what do you think about enabling options like -fsanitize=address when building rats-tls-server and rats-tls-client? I think this way we can detect obvious memory issues when running CI actions. You might consider this as another PR.

[haosanzi]

LGTM. Please follow this link to fix your commit header.