Loader Contexts

[dwoz]

What does this PR do?

Adds loader contexts so that multiple loaders can't stomp on each other.

What issues does this PR fix or reference?

Prior to these changes salt's 'magic attributes' (__utils__, __salt__, __opts__, ect..). Would be added as global attributes to a s loaded module's namespace. This had the un-intended side effect of allowing a method call from one loader to change something in another loader. This can be particularly problematic for __context__ and __opts__. This can also cause problems for loaders added with unique configs.

There is also an addition of a new pack_self attribute to Salt's LazyLoader class. This allows the loader to expose itself as a magic dunder without creating circular references on in the loader's pack dictionary. Those circular references are the cause of some memory leaks. The pack_self argument should be used to avoid memory leaks.

Previous Behavior

Due to the global nature of Salt's dunder methods, calls from one loader could interfere with other loaders.

New Behavior

Loaders use contextvars to provide a context that is specific the the loader that loads the function being called.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs - More needed
• Changelog - Still Needed
• Tests written/updated - More needed

[s0undt3ch]

The new requirement should be added to requirements/static/pkg since it will become a hard dependency, in fact, it should actually be added to requirements/base.txt since its a hard dependency and applies to all platforms.

[s0undt3ch]

There are still a lot of print debug statements, but you should know that already.
Left some questions.

[oeuftete]

Approving based on others', and that I know this fixes #54045.