internal: remove circular dependencies

[DifferentialOrange]

This PR removes existing circular dependencies in module, as well as remaining requires inside the functions.

Before:

After:

(Still seems confusing, but at least more hierarchic.)

It is a prerequirement to metrics.cfg{} reload support.

I didn't forget about

• Tests (still green)
• Changelog (internal)
• Documentation (README and rst) (internal)
• [x] Rockspec and rpm spec

Closes #433, part of tarantool/tarantool#7725

[yngvar-antonsson]

Is this schema handmade or generated?

[DifferentialOrange]

Is this schema handmade or generated?

I didn't even though that it is possible to automatize the process, so it's hand-made with app.diagrams.net . (I can share the sources if you need them.)