Global IORuntime threadpools are not closed in tests, causing a resource leak

This library uses IORuntime.global for tests, which causes it to never close the threadpools that are created by this global IORuntime. Combined with sbt creating a new classloader for every test run and every submodule, this results in a lot of IORuntimes and threadpools being created and never cleaned up. Eventually, it causes sbt to run of out memory after a number of test runs, especially in projects with many submodules.

I'm not sure what the best approach would be to avoid this issue, as creating a new IORuntime in every test suite will probably slow down running tests?

Start by tracing how test suites obtain IORuntime.global and how sbt creates classloaders across test runs and submodules. Compare the resource lifetime of that global runtime with the cost of creating runtimes per suite. Done means repeated test runs no longer retain threadpools or eventually exhaust memory, without an unacceptable test-running slowdown.