Adapted NN generation to n3fit update

[ElieHammou]

This PR addresses the issue #24.

I have imported the new ReplicaSettings class and created an instance of it for _pdfNN_layer_generator to use as an argument.

Another issue was caused by the function write_exportgrid from colibri.export_results which was expecting Q0 as an argument rather than Q. I have fixed this as well.

Note that there is still a mismatch between the previous keys (initializer_name and layer_type), still present in the example runcard, and the new ones expected by ReplicaSettings (initializer and layer_type). It could be nice to harmonise this before merging but it is purely cosmetic:

    replicas_settings = [
        ReplicaSettings(
            nodes=nodes,
            activations=activations,
            initializer=initializer_name,
            architecture=layer_type,
            seed=seed,
        )

The fixes were successfully test on the example POD runcard.

[Copilot]

Pull request overview

This PR adapts the codebase to work with an updated n3fit API by migrating from passing individual parameters to _pdfNN_layer_generator to using the new ReplicaSettings class, and correcting a parameter name in write_exportgrid calls.

Key Changes:

• Imports and uses the new ReplicaSettings class from n3fit.model_gen to configure neural network replicas
• Updates _pdfNN_layer_generator function call to accept replicas_settings instead of individual parameters (nodes, activations, initializer_name, layer_type, seed, impose_sumrule, num_replicas)
• Fixes parameter name from Q to Q0 in write_exportgrid function calls

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[ElieHammou]

The build test has failed because the right version of eko could not be found with python 3.11.
I installed my environment with the file from the repo and it gave me python 3.12.12 so I am not sure why the test points to 3.11

[LucaMantani]

Looks good to me! Thanks @ElieHammou

[comane]

Looks good to me, thanks for fixing it