Add smartptrs and atomics

[planetis-m]

So this PR add smartptrs after passing a review round here nim-lang/Nim#18450
They now depend on new atomics #4 Other changes include the addition of newSharePtr/newUniquePtr without data parameter and the accompanying []= overloads. As discussed nim-lang/Nim#18450 (comment)

Bug planetis-m/sync#13 affects pointers that contain ref objects, only when the user tries to reference them in a local variable let a: ref Foo = mysharedptr[] not sure how to disallow this.

[planetis-m]

Unrelated?

 /home/runner/work/threading/threading/nim/lib/nimbase.h:542:1: note: in expansion of macro ‘NIM_STATIC_ASSERT’
 NIM_STATIC_ASSERT(sizeof(NI) == sizeof(void*) && NIM_INTBITS == sizeof(NI)*8, "");
 ^~~~~~~~~~~~~~~~~
In file included from /home/runner/.cache/nim/tatomics_d/stdlib_assertions.nim.c:11:0:
/home/runner/work/threading/threading/nim/lib/nimbase.h:271:35: error: static assertion failed: ""
 #define NIM_STATIC_ASSERT(x, msg) _Static_assert((x), msg)
                                   ^
/home/runner/work/threading/threading/nim/lib/nimbase.h:542:1: note: in expansion of macro ‘NIM_STATIC_ASSERT’
 NIM_STATIC_ASSERT(sizeof(NI) == sizeof(void*) && NIM_INTBITS == sizeof(NI)*8, "");
 ^~~~~~~~~~~~~~~~~

[narimiran]

Unrelated?

Yes, it was there before. We need to look into that separately.

[Araq]

I'm merging this, other CI failures can be fixed later.