Correctly fail to parse list-of-oneOf with an invalid item

[ddadamhooper]

What does this PR do?

Correctly fails to parse a FormulaAndFunctionEventQueryDefinition when it contains an invalid group_by list entry.

The code generator was failing to propagate unparsed from a oneOf to its parent in this case.

(DataDog's APIs don't generally return invalid objects, so this shouldn't affect users. The value comes with an upcoming PR, where a oneOf item contains a list which contains another oneOf item. In that case, we need to detect invalid objects from the inner oneOf.)

Review checklist

Please check relevant items below:

• This PR includes all newly recorded cassettes for any modified tests.
• This PR does not rely on API client schema changes.
  • The CI should be fully passing.
• Or, this PR relies on API schema changes and this is a Draft PR that includes tests.
  • Note: CI shouldn't be run on this Draft PR, as its expected to fail without the corresponding schema changes.

[ddadamhooper]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Propagate unparsed through the oneOf group_by wrapper

In the event-query path, group_by is a FormulaAndFunctionEventQueryGroupByConfig oneOf wrapper; its deserializer stores the List<FormulaAndFunctionEventQueryGroupBy> variant and increments match without checking whether any list item has unparsed=true, so this added copy still sees groupBy.unparsed == false. A payload such as group_by: [{facet: "@x", sort: {aggregation: "NOT_A_VALID_AGGREGATION"}}] therefore leaves FormulaAndFunctionEventQueryDefinition parsed even though the child sort is invalid; the new test covers the UserJourney model's direct list, not this oneOf wrapper.

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[jack-edmonds-dd]

approval for modelSimple.j2 (I'm assuming the rest of the changes are generated).