Implement test filtering

[razzeee]

elm-test-rs implements --filter

I think we will end up using this to be able to run/rerun a specific test without rerunning all tests.
This is especially interesting for GUI based tools like test explorers like https://github.com/frawa/vscode-elm-test-runner

[razzeee]

Whoops, I guess this is a new version of #504

Sorry for the noise, I seem to be a bit distracted

[Yabasa]

I'm new to Elm and loving the ecosystem with these awesome high-quality tools. I too would love to see this. In my case I'm looking at writing a neotest adapter for elm-test so you can run individual tests from Neovim. Very useful when you're focusing on making a small subset of tests pass. I imagine this would be useful for all editors that support targeted test execution.