Support :only option for running single ns or var

[borkdude]

For people used to leiningen, the :only option can be convenient to run either a whole namespace or a single test from a namespace.

Especially when paired with error reporting, where :only foo.bar/baz-test is printed when foo.bar/baz-test is failing, so you can copy paste that in the command line.

I did not include the printing in this PR, but can do another PR if that seems a good idea.

[puredanger]

• In the case of :only a-ns, if used in combination with a :patterns option (often the case in a deps.edn usage), that is used in the ns-filter and all namespaces are included instead of just the :only one.
• In the case of :only a-ns/a-var, the namespace doesn't get required and the var can't be found.
• There are also some incidental whitespace changes that should not be included.

I find myself a bit on the fence about this change as it is already covered by use of the existing :nses '[a-ns]' or :vars '[a-ns/a-var]' (although the first of those has the same issue with :patterns), and since these are both collection options they are definitely more onerous on the user to handle the quoting. I would still be willing to merge this, but the above issues need to be addressed.

[borkdude]

@puredanger Addressed in new commit:

• undo whitespace changes
• clear :namespace-pattern option when :only is used
• move option normalization inside the test function so it's not specific to -M or -X usage
• add tests for :only

In the case of :only a-ns/a-var, the namespace doesn't get required and the var can't be found.

I could not reproduce that, I can see the namespace appear in :nses that are to be required in the test function and this is why I added a test for the only behaviour which does not seem to exhibit the bug.

[borkdude]

As this option is considered "on the fence", I'm closing this. neil test :only ... is now supported which forwards the argument to the cognitect test runner either as -v or as -n.