Phase-slope index using spectral_connectivity_time instead of spectral_connectivity_epochs

[seqasim]

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PR Description

Currently, the function for computing phase-slope index is hard-coded to be computed over epochs to produce time-resolved PSI, and there's no option for computing the phase-slope index over time to produce PSI per epoch. This would be useful if you think the average directionality between two signals over the entire timecourse is informative. You could compute this by binning your trials into categories (i.e. good trials v. bad trials) and then computing PSI, but there's no way to compute PSI per epoch and relate it to continuous trial-level predictors.

Here, I add a new function phase_slope_index_time to mne_connectivity.effective that compute PSI over time. I should note that I wasn't able to test this function directly as I'm having trouble getting the forked repo installed, in editable mode, with all necessary dependencies, but have written a test function in tests.test_effective to facilitate this.

Merge checklist

Maintainer, please confirm the following before merging:

• All comments resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• PR description includes phrase "closes <#issue-number>"