feat: support unions when building private queries

[mjfaga]

Description

Address a bug where inline fragments on Union types are not properly respected when re-resolving a partial query for a specific field in the query request.

Type of Change

• [x] Bug Fix
• [ ] New Feature
• [ ] Breaking Change
• [ ] Refactor
• [ ] Documentation
• [ ] Other (please describe)

Checklist

• [x] I have read the contributing guidelines
• [x] Existing issues have been referenced (where applicable)
• [x] I have verified this change is not present in other open pull requests
• [x] Functionality is documented
• [x] All code style checks pass
• [x] New code contribution is covered by automated tests
• [x] All new and existing tests pass

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9ae05a8) 94.45% compared to head (a09a02d) 94.40%.

Files	Patch %	Lines
src/ApolloServerManager.ts	90.90%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #34 +/- ## ========================================== - Coverage 94.45% 94.40% -0.06% ========================================== Files 13 13 Lines 487 500 +13 Branches 148 152 +4 ========================================== + Hits 460 472 +12 - Misses 27 28 +1 ```

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