Adding threads to Trove can cause errors if thread is of running or normal status

[Sleitnick]

Troves accept threads that will be closed when the trove is cleaned up. However, if this thread is the currently-running thread or marked as the "normal" thread, then it will throw an error. Here are a couple repros:

trove:Add(coroutine.running())
trove:Clean()
-- Error: cannot close running coroutine

trove:Add(coroutine.running())
task.spawn(function()
	trove:Clean()
end)
-- Error: cannot close normal coroutine

A thread that is in the "running" state means that it is the currently-active coroutine. A thread that is in the "normal" state means that it has resumed another coroutine and is awaiting that coroutine to yield back.

Thus, another example of the "normal coroutine" error would be such:

local thread1, thread2

thread1 = coroutine.create(function()
	trove:Clean()
end)

thread2 = coroutine.create(function()
	trove:Add(thread2)
	task.spawn(thread1)
end)

task.spawn(thread2)
-- Error: cannot close normal coroutine

---

And thus comes the question: How should Trove handle this? Should it just have better error messaging? Ideally, developers should only be placing threads into a Trove that they know will be fine to be closed. Simply checking the thread status on Add won't cut it, because that would assume that Clean would be called from the same thread that Add was called, which may not be the case.