[ENH] Integrate trials object with Fano factor

[Moritz-Alexander-Kern]

This pull request introduces an enhancement to Fano factor using the the elephant.trials module to represent trials. This change is part of a greater effort to provide a more structured and unified approach for handling trial data in Elephant.

Trial representations

• trial object: The new trial_object is now used as the primary input structure for representing trials. This object handles trial data, see https://elephant.readthedocs.io/en/latest/reference/trials.html .

This pull request adds two new parameters, pool_trials and pool_spike_trains, to the function. These parameters allow to control how spike trains are aggregated across trials and within individual trials.

Changes

• fanofactor now handles trial object
• added tests to test Trial object input
• Added pool_trials parameter
• Added pool_spike_trains parameter

[coveralls]

coverage: 88.268% (-0.1%) from 88.401% when pulling 6bb2fc3b42ffa842aff191ae0f311fedafcb9c4f on INM-6:enh/trials_fano_factor into 123ca040b11a5961643c4de080df89af9b1fcd24 on NeuralEnsemble:master.