Stop active execution

there are certain cases where an execution might run indefinitely or simply hang by a logic mistake,

### Repro example
`dotnet-repl --default-kernel fsharp`
```fsharp
#r "nuget: Suave"
open Suave
startWebServer defaultConfig (Successful.OK "Hello World!")
```
after you hit enter a "Suave" web server is running which steals the interactive session you need to close the terminal otherwise it won't stop until for some reason it fails.

this is an awesome project by the way I already love it!

No files or tests are named in the issue. Start by running the `dotnet-repl --default-kernel fsharp` example with the Suave web server, then determine how active execution can be stopped without closing the terminal; done means the interactive session remains usable after stopping it.

Written by the indexing model from the issue text.