Remove IO from close function

[aviks]

This function is called from the finalizer as of 74ce7df

Tentative fix for #44 but I'm not 100% sure that's enough. But hopefully this helps.

[ancapdev]

What about the lock, is that safe? If the lock is taken, the task is put in the wait queue, and it yields.

[ancapdev]

According to the manual, locks are not safe to take in finalizers: https://docs.julialang.org/en/v1/devdocs/locks/#Locks

There's some discussion here: https://discourse.julialang.org/t/acquiring-locks-in-finalizers/119628/3

Links example code for working around the general unsafety of locks in finalizers, here: https://github.com/JuliaMath/FFTW.jl/blob/f888022d7a1ff78491abf8f33f1055cc52a68f0a/src/fft.jl#L351-L381

[aviks]

Yes, indeed, the locks seemingly need fixing if this is called from a finalizer. I've taken a detour to fix the tests (#47) since it was annoying to work on any changes when the tests failed for other reasons. I'll get back to this after that.

It would be nice to get a reproducer for #44 -- it's scary to be doing major surgery to multithreaded code without a reproducer.

[aviks]

Closed in favour of #48