Implement InputDelayESN

[MarcoCerino23]

Description

This PR implements the InputDelayESN model as requested in #314.

Key Changes:

• New Model: Added InputDelayESN in src/models/esn_inputdelay.jl.
• Architecture: The model is composed of a DelayLayer (acting as an input modifier), an ESNCell, and a LinearReadout.
• Mathematical implementation:
  • Input expansion: $\mathbf{u}_{\mathrm{d}}(t) = [\mathbf{u}(t), \mathbf{u}(t-s), \dots, \mathbf{u}(t-Ds)]^T$
  • Reservoir update: $\mathbf{x}(t) = (1-\alpha) \mathbf{x}(t-1) + \alpha \phi(\mathbf{W}_{\text{in}}\mathbf{z}(t) + \mathbf{W}_r\mathbf{x}(t-1) + \mathbf{b})$
• Testing: Added test/models/test_esn_inputdelay.jl to verify correct constructor wiring, parameter dimensions, and consistency with the AbstractEchoStateNetwork interface using outputsize.

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• Any new documentation only uses public API

Additional context

This PR addresses the first part of the requirements outlined in issue #314.

[MarcoCerino23]

Thanks. I have finalized the InputDelayESN implementation following the feedback: internal DelayLayer for a batteries-included approach and exposed states_modifiers for flexibility. I've also merged the latest changes from the remote branch.

[MartinuzziFrancesco]

Nice, thanks! just a couple of minor naming things and we can merge this. Feel free to up the version too

[MarcoCerino23]

Thanks Francesco! I'm already bumping the version to 0.12.14 in Project.toml.
Regarding the naming: could you please specify which names you'd like me to change? I couldn't find the inline comments in the 'Files changed' tab. Let me know and I'll update the code immediately.

[MartinuzziFrancesco]

you can remove the _wrap_layers here, since we have just the DelayLayer

[MartinuzziFrancesco]

maybe change name to input_delay, we just pass the single layer here

[MartinuzziFrancesco]

my bad, I didn't submit the review earlier. can you see them now?