Fallback IOLocal#unsafeThreadLocal by a true ThreadLocal

[armanbilge]

tl;dr is that for the IOLocalContextStorage in typelevel/otel4s#214 to work for arbitrary Java libraries, it must properly implement the ContextStorage API even when used in a context outside of IOFiber. To accomplish this, we can make ThreadLocals returned by IOLocal#unsafeThreadLocal behave as a true ThreadLocal when used outside of an IOFiber. This is not currently possible to implement in userland because there is no way to know if you are currently running in a fiber or not.

[djspiewak]

This is pretty evil. :( Also remember the only way you could get an IOLocal in the first place in this type of situation is if you created one inside of IO or unsafely and then yolo'd it out into thread land.