support parallel execution

[scarf005]

sbt parallelizes munit tests but scala-cli won't be able to parallelize munit tests. as scala-cli is included as default scala toolkit, supporting parallel execution will be beneficial to new users.

[tgodzik]

Thanks for reporting! I am not sure what we need to do to support it. We would need to dig in if we decide it's worth pursuing

[SethTisue]

@scarf005 seems like a scala-cli ticket rather than an MUnit ticket? it's not actionable on the MUnit side, is it? (do I misunderstand somehow?)