Mark entities as unchanged when matched by entities loaded from database

[AndriySvyryd]

Fixes #35762

[Copilot]

Pull request overview

This PR fixes EF Core tracking behavior during explicit loading/tracking queries so that when a query result matches an entity already tracked as Added (same key), the tracked entity is corrected to Unchanged rather than later being re-inserted and causing duplicate-key failures (issue #35762).

Changes:

• Update query identity-resolution (QueryContext.TryGetEntry) to transition matching Added entries to Unchanged.
• Add a new SQLite functional test covering the scenario where Load() matches an Added entity that already exists in the store.
• Tighten specification tests to assert that entities materialized/associated by Load() are tracked as Unchanged (unless the graph is detached).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/EFCore.Sqlite.FunctionalTests/LoadExistingEntityStateSqliteTest.cs	Adds regression test for explicit-load correcting Added to Unchanged when the entity exists in the database.
test/EFCore.Specification.Tests/LoadTestBase.cs	Adds assertions verifying loaded entities end up Unchanged (or Detached when appropriate).
src/EFCore/Query/QueryContext.cs	Implements the core behavior change: Added entry matched by a tracking query is set to Unchanged.
src/EFCore/Internal/EntityFinder.cs	Removes an unused using.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.