Add generalization of delays between recurrent and readout layers

[JesusEV]

This PR proposal aims to enhance the flexibility of delays between the recurrent-to-readout and readout-to-recurrent layers.

TODOs:

• [ ] Discuss the necessity of defining delay_rec_out and delay_out_rec as configurable parameters in neuron models.
• [ ] Address potential conflicts between the parameters delay_rec_out, delay_out_rec and the hardcoded equivalents in eprop_archiving_node.
• [ ] Consult with the HEP on optimal strategies for buffering learning signals when delay_out_rec > 1.
• [ ] Review the function pointer *update_pre_syn_buffer and its parameters for potential improvements.
• [ ] Complete the missing items in the documentation.

[github-actions[bot]]

Pull request automatically marked stale!