Fix loader batching logic in defineLoader + upgrade dependencies and GraphiQL

[acoBOYZ]

Fix internal defineLoader batching issue + dependency & GraphiQL updates

This pull request fixes a problem in Mercurius' internal defineLoader function, where GraphQL field loaders were being called once per item, instead of once per field with batching.

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✅ What was fixed

The problem was caused by using complex objects ({ obj, params }) as loader keys, which prevented Mercurius from recognizing repeated calls as "the same".

We now use a serialize() function that:

• Uses obj.id and params.lang to create a fast and consistent batching key
• Falls back to JSON.stringify({ obj, params }) if id is not available

We use id because it's a commonly used identifier in GraphQL schemas, and it's much faster than serializing the entire object.

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✅ Also included

• Upgraded all dependencies to their latest stable versions
• Updated GraphiQL static files (main.js, config.js) to the latest version

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🧪 Real-world test results (k6)

Before (no batching):

• ~122ms average response time
• Loader was called many times per query

After (with batching):

• ~37ms average response time
• Loader is called only once, with all keys batched
• ~70% performance improvement confirmed under load

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🔒 Notes

• This fix is applied internally, users do not need to change how they define their own loaders.
• It's safe and backward-compatible.

[mcollina]

Can you add some tests as well?

[mcollina]

I don't think this is generic enough to be included in the library. How about you add a a way to include a custom serializer for the loader instead?

[acoBOYZ]

You are right. I found a better way to handle it. Also i will add some tests for it. After that if you like it can pr docs for that too. I will publish it soon