feat:🎁🧪 run tests directly from buffer

[GustavEikaas]

Tasks

• [x] Add gutter sign for running test
• [x] Add keybind for run
• [ ] Get end-line from discovery so you can run test from the entire declaration (Optional)
• [x] Update gutter sign when test is finished (complicated with ClassData)
• [x] Add experimental configuration flag
• [x] Update readme
• [ ] Add some trigger for discovery outside the testrunner window