Namespace JSON schema helpers under JSON ingestion

[jwils]

Why

After the move-only PR preserves rename detection, put the moved helper constants under the ElasticGraph::JSONIngestion namespace.

What

• Namespace the moved JSON Schema helper classes and RBS signatures
• Update schema_definition references and tests to use the new qualified constants

Risk Assessment

Medium - namespace-only behavior should be unchanged, but it updates call sites across schema_definition.

References

• Stacked on Move JSON schema helpers to json ingestion gem #1201.
• Local lint, type check, schema artifact checks, and documentation coverage passed while building this split.

[myronmarston]

I'd encourage you to do the typical nesting thing:

module ElasticGraph
  module JSONIngestion
    # ...
  end
end

It'll require you to indent every line but I can just ignore whitespace when reviewing and it'll hide lines with indentation-only changes. (Note: ignoring white space doesn't help when moving files as it appears that git's whitespace-ignoring feature doesn't apply to its file movement detection. That's why it's so nice to defer changing the indentation until the files have already moved.)

Besides being in line with how we write code everywhere else, it allows the code in the module to directly reference ElasticGraph:: constants, removing the need to prefix them with ::ElasticGraph as you've done here. That in turn leads to a smaller whitespace-ignored diff to review, and creates nicer code in the long run.

[myronmarston]

Would be nice to not remove comments unless they are inaccurate.