Add 'strict' Suite

MUnit allows overriding a TestValue to a value to enforce a test always returns that type. In the example it is used for Future.

Due to the lazy evaluation of IO I think it'd be very useful if I could enforce my test would always return an IO to prevent code from never being run. ScalaTest has recently changed their suites to be AnySpec (can return Any) or AsyncSpec (must return a Future). munit-cats-effect could introduce something similar for returned IO's by overriding MUnit's TestValue.

If added to munits-cats-effect, users should probably still have a choice (just like in ScalaTest) between the two styles. And maybe 'strict' should not be the default? I don't have a strong opinion on what the naming should be.

For implementation some refactoring would probably be needed. TestType is made final in munit.FunSuite so the new suite would have to extend from munit.Suite. Code sharing between the two styles is probably also wanted. I'd be interested in helping out with a PR if this is wanted

Start by reading MUnit's TestValue and the existing munit-cats-effect suite implementation. Check how munit.FunSuite and munit.Suite differ, especially around the final TestType, and review the ScalaTest AnySpec and AsyncSpec comparison. Done means a selectable strict IO-returning suite exists alongside the current style, with shared behavior preserved and tests covering both choices.