Resolve "Split out recursive namespace traversal"

What does this MR do?

Moved the set of Namespace methods that deal with traversal in to their own module.

This move is being made as part of a larger effort to improve performance of namespace queries by replacing recursive queries with linear queries.

There is some more general information in the epic at &5296 (closed)

The work has been created under a new module to satisfy this new rubocop rule !51236 (merged)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #300519 (closed)