refactor: refactor child context to be child context return data

[Eikix]

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Resolves: #387

What is the new behavior?

• Each context has only a parent context field that tracks its parent inside a Nullable smart pointer
• Instead of having a child context field, it simply has a child_context_return_data

Does this introduce a breaking change?

• Yes
• No

[enitrat]

LGTM - Can you add some info in the docs about this design choice later?

[enitrat]

lfg