fix(10.x.x): keep SynchronizedDataLoader when the registry has an instrumentation, and synchronize loadMany.

[eocantu]

📝 Description

SynchronizedDataLoader (#2202) has two gaps that let concurrent loads on a cached, non-batching loader call the downstream more than once:

• DataLoaderRegistry rebuilds each loader with transform(...) to add its name and instrumentation. DelegatingDataLoader.transform returns the plain delegate, so the wrapper is lost whenever a DataLoaderInstrumentation is passed to generate(...), which is always the case with SYNC_EXHAUSTION. transform now re-wraps the result.
• loadMany bypasses the wrapper and calls the delegate's loadImpl directly. That includes getValuesFromDataLoader. The three loadMany overloads are now synchronized like load.

🔗 Related Issues

Follow-up to #2202, which addressed the loss of load synchronization