feat: update to graphql-java 25

[samuelAndalon]

📝 Description

• Update com.graphql-java:graphql-java from 24.3 to 25.0
• Update com.graphql-java:java-dataloader from 4.0.0 to 6.0.0
• Update com.apollographql.federation:federation-graphql-java-support from 5.5.0 to 6.0.0

GraphQL Java 25 introduced stricter JSpecify nullness and changed parts of subscription/DataLoader execution. This required updates around nullable AST values, DataFetchingEnvironment#getSource, DataFetcherResult builders, APQ marker handling, and DataLoader helper casts.
FlowSubscriptionExecutionStrategy was refreshed to match GraphQL Java 25’s subscription execution behavior, including FetchedValue unwrapping, per-event AlternativeCallContext, and DataLoader dispatch hooks.

A GraphQL Java issue was opened for the DataFetchingEnvironment#getDataLoader nullable value type mismatch in Kotlin: graphql-java/graphql-java#4374

[github-actions]

Apollo Federation Subgraph Compatibility Results

Federation 1 Support	Federation 2 Support
_service 🟢 @key (single) 🟢 @key (multi) 🟢 @key (composite) 🟢 repeatable @key 🟢 @requires 🟢 @provides 🟢 federated tracing 🟢	@link 🟢 @shareable 🟢 @tag 🟢 @override 🟢 @inaccessible 🟢 @composeDirective 🟢 @interfaceObject 🟢

Learn more:

• Apollo Federation Subgraph Specification
• Compatibility Tests