Fix QueryContext<T> dropping sort fields after a nested object field

[glen-84]

Summary

• QueryContext<T>.Sorting now contains every field of the order argument when a field follows a nested object field, such as { author: { name: ASC }, title: ASC }, the list form [{ author: { name: ASC } }, { title: ASC }], or the same shape one level deeper. Those fields were dropped without an error, and a field sharing a name with one inside the nested object ({ author: { id: ASC }, id: ASC }) threw.
• The formatter behind ISortingContext.AsSortDefinition<T>() resolved each field a second time when leaving it, against the nested object's type, so that type was never popped and every later field was looked up on it. It now resolves the field once on entry and reuses it on leave.

Test plan

• New SortingContextTests cases assert the sort definition for each of those shapes, plus a scalar field before a nested object. All of them except the scalar-first case fail without the fix.
• Data.Sorting.Tests passes.
• Every test in Data.Tests and Data.PostgreSQL.Tests passes, which covers QueryContext sorting against PostgreSQL.

Closes #10489

[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved review comments remain, and regression coverage is included.

Review effort: Lite
Findings: None

What changed in this PR

Fixes nested sorting so fields following nested object fields are preserved in QueryContext<T>.

Changes:

• Corrects field and type-stack handling during sort-definition formatting.
• Adds regression tests for nested, list, duplicate-name, and deeper nested sorting.

File	Summary
src/​HotChocolate/​Data/​test/​Data.Sorting.Tests/​Context/​SortingContextTests.cs	Adds regression coverage for affected sorting shapes.
src/​HotChocolate/​Data/​src/​Data/​Sorting/​Context/​SortingContext.cs	Preserves resolved fields across nested formatter traversal.

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[github-actions]

Patch coverage

83.3% of changed lines covered (5/6)

File	Covered	Changed	Patch %
…/HotChocolate/Data/src/Data/Sorting/Context/SortingContext.cs	5	6	83.3% 🟡

Uncovered changed lines (JSON)

{
  "sha": "14b7f3e28722de040fbf06ceef1f4b79e1bf16e4",
  "files": [
    { "path": "src/HotChocolate/Data/src/Data/Sorting/Context/SortingContext.cs", "ranges": [[162, 162]] }
  ]
}

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Project coverage: 58.5% (313849/536121 lines)