Fix optional complex property default values tracking

[Copilot]

Fixes #37386

When optional complex properties transition from null to non-null with default-valued properties (e.g., new LockInfo(default(DateTimeOffset))), those default values were not being tracked or saved to the database.

Changes

• Change Detection: Enhanced ChangeDetector.PropertyChanged to detect when non-collection complex properties transition from null to non-null (using switch statement pattern)
• Property Modification: When a complex property changes from null to non-null, all saveable inner properties are now marked as modified to ensure they are persisted (even with default values)
• Null Checks: Using pattern matching (is null, is not null) to avoid issues with overridden equality operators
• Test Coverage: Added comprehensive tests for optional complex properties with default values
• Test Infrastructure: Updated ExecuteWithStrategyInTransactionAsync to support 4 nested test operations in base class and all derived test classes (InMemory and Cosmos)
• Cosmos Configuration: Added partition key configuration for test entities
• Provider Limitations: Properly skipped tests for provider-specific limitations (InMemory issue Fully support complex types with the InMemory provider #31464, Cosmos issue Add Cosmos support for complex types #31253)

Testing

• ✅ All API consistency tests pass
• ✅ Sqlite tests pass including discriminator and multi-property tests
• ✅ Existing tests pass, confirming the fix doesn't break existing functionality
• ✅ InMemory multi-property test is properly skipped due to provider limitation (issue Fully support complex types with the InMemory provider #31464)
• ✅ Cosmos multi-property test is properly skipped due to optional complex properties not being supported (issue Add Cosmos support for complex types #31253)
• ✅ Cosmos tests build successfully with proper partition key configuration

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[Copilot]

Pull request overview

This PR fixes issue #37386 where default values in optional complex properties were not being tracked or saved to the database when the complex property transitions from null to a non-null value with default-valued properties.

Key Changes

• Enhanced change detection logic to detect when nullable complex properties transition between null and non-null states
• When a complex property changes from null to non-null, all inner properties are now marked as modified to ensure they are persisted (even with default values)
• Added comprehensive test coverage for the scenario with multiple properties having default values

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/EFCore/ChangeTracking/Internal/ChangeDetector.cs	Added DetectComplexPropertyChange method to detect null/non-null transitions and mark inner properties as modified; integrated this detection into both PropertyChanged and LocalDetectChanges methods
test/EFCore.Specification.Tests/ComplexTypesTrackingTestBase.cs	Added test Can_save_default_values_in_optional_complex_property_with_multiple_properties with entity and complex type definitions; updated ExecuteWithStrategyInTransactionAsync signature to support a third nested operation
test/EFCore.SqlServer.FunctionalTests/ComplexTypesTrackingSqlServerTest.cs	Skipped the new test for proxies fixture since complex types with notification change tracking are not yet supported (Issue #36175)

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.