Allow expensive tests to be disabled

[niklasdewally]

Summary

Allow the selection of which tests to run depending on how expensive (time consuming they are). This should take the form of a flag to the tester. For example, in Conjure, --limit_time=5 runs only those tests that have an expected run time of <=5 seconds.

CI should be modified to run both a quick version of the tests, and all the tests.

Background

In #572, I proposed using Rust's builtin #[ignore] attribute 1 to disable by default a test case that took too long to run.

However, we want a more fine grained approach to select which tests to run than whether a test is ignored or not.

Oz suggested the following:

I like the idea of having infrastructure to select which test to run depending on how expensive the test is though. In Conjure I optionally add a rough expected time (in seconds) for each test case. Then running --limit_time=5 runs only those tests that have an expected run time of <=5 seconds. Default value is 0.

Could be better than the coarse grained quick/all. Quick can then be an alias for <=1 or whatever and all can be actually all.

[niklasdewally]

CC: @EEJDempster @Soph1514 @ozgurakgun