Stabilize @defer overlap HTTP tests with instant initial fields

[glen-84]

Summary

• DeferOverHttpTests.Defer_Overlap_*_Legacy_Format flaked because the initial selection included description, whose 1000 ms resolver delay raced the deferred fragment's payload — the engine non-deterministically bundled the initial and deferred @defer payloads into one instead of two. The xUnit 3 / Microsoft Testing Platform migration shifted scheduling and exposed this pre-existing race.
• Aligned the overlap tests with the pattern used by every other (non-flaky) defer test: the initial selection now contains only the instant name field, while the slow description field stays inside the @defer fragment. The initial payload flushes immediately and the deferred payload reliably lags, so delivery is deterministically two parts.
• No resolver delays were changed. Only the initial-payload snapshots were updated (they drop description); the merged incremental payloads are unchanged, so the legacy merge/dedup behavior is still covered via the name overlap.

Test plan

• Ran the three overlap tests 20× in a loop: green every iteration.
• Ran the full DeferOverHttpTests class (63 tests): all pass.

[Copilot]

Pull request overview

This PR stabilizes the legacy-format @defer overlap HTTP tests by ensuring the initial payload contains only fields that resolve immediately, avoiding nondeterministic bundling of initial and deferred payloads.

Changes:

• Updated the overlap test queries so the initial selection only requests product { name }, keeping the slow description field inside the deferred fragment.
• Updated legacy-format response expectations/snapshots so the initial payload no longer includes description while the deferred incremental payload remains unchanged.

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