Add key inferrence for lookups

[michaelstaib]

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[Copilot]

Pull request overview

This PR adds automatic @key directive inference for source schemas by deriving entity key selection sets from @lookup field arguments (including @is field selection maps), so published source schemas better describe resolvable entity keys.

Changes:

• Introduces SourceSchemaKeyInferenceTypeInterceptor to infer and apply @key(fields: ...) directives to lookup return types (and relevant possible types).
• Updates the @key directive definition to be repeatable, enabling multiple inferred/manual keys on the same type.
• Adds a new schema option (InferKeysFromLookups) and enables it by default via AddSourceSchemaDefaults, while registering the interceptor in the default executor builder.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/HotChocolate/Core/src/Types/Types/Composite/SourceSchemaKeyInferenceTypeInterceptor.cs	New interceptor that collects @lookup fields and applies inferred, deduplicated @key directives to target types.
src/HotChocolate/Core/src/Types/Types/Composite/Directives/EntityKey.cs	Makes @key repeatable to support multiple keys (manual + inferred) on OBJECT/INTERFACE.
src/HotChocolate/Core/src/Types/SchemaOptions.cs	Adds InferKeysFromLookups option and copies it in FromOptions.
src/HotChocolate/Core/src/Types/IReadOnlySchemaOptions.cs	Adds InferKeysFromLookups option to the read-only schema options API surface.
src/HotChocolate/Core/src/Types/Execution/DependencyInjection/RequestExecutorServiceCollectionExtensions.cs	Registers the new interceptor (gated by the new option).
src/HotChocolate/Core/src/Types/Execution/DependencyInjection/RequestExecutorBuilderExtensions.Composite.cs	Enables key inference by default for source schema defaults.

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