Add gastropy.neuro.eeg and gastropy.neuro.meg modules

[micahgallen]

Summary

Implement EEG and MEG sub-modules within gastropy.neuro for gastric-brain coupling analysis with electrophysiological data.

Scope

EEG (gastropy.neuro.eeg)

• EEG-EGG phase synchrony computation
• Frequency-band specific coupling (e.g., gastric-alpha, gastric-theta)
• Sensor-level and source-level PLV

MEG (gastropy.neuro.meg)

• MEG-EGG coupling analysis
• Source localization integration
• Sensor-level PLV maps

Design Notes

• Should follow the same layered pattern as gastropy.neuro.fmri: thin wrappers that call into the modality-agnostic gastropy.coupling module.
• MNE-Python is the natural dependency for EEG/MEG I/O and preprocessing.
• Empty placeholder modules already exist at gastropy/neuro/eeg.py and gastropy/neuro/meg.py.

Related

Part of the JOSS submission roadmap (JOSS_ROADMAP.md).