implement `rtx test`

[jdx]

asdf has the ability to test a plugin, we should do the same for parity: https://asdf-vm.com/plugins/create.html#testing-plugins

This will also help with #182

[jdx]

this command doesn't actually do what I thought it did. Somehow I thought that it would call a binary in the plugin like bin/test so the plugin could perform some checks. It's more manual, and just makes it easier to install a plugin and runtime at the same time which is already pretty easy to do with rtx exec.

That said, it has the ability to use a specific git ref which you can't do with rtx exec. I suspect it might be possible to add this but I'm not sure what the syntax would be. A less good workaround would just be if I implemented the ability to set git refs with plugins install or maybe plugins update.

I'm wondering if it would be better see if asdf might be interested in adding a bin/test feature to the plugins like I was thinking.

[jdx]

this seems to be of less value to me as I explained in #192

I'd be open to adding this if someone can give me a use-case where it is important though. It seems more useful in asdf since there isn't the ability to install a plugin, runtime, and execute in a single command like we can do in rtx