Phase 1: core MNE wrapper (single-model)

[neuromechanist]

Part of #139.

An MNE-facing wrapper (optional pyAMICA[mne] extra, same lazy-import pattern
as the optional mlx extra so import pyAMICA never requires MNE) that fits
directly from mne.io.Raw/Epochs (picks=...) and interoperates with the
standard MNE ICA consumer surface (.apply(), component access, mne.viz
component plotting) for the single-model case.

Reference (architecture only, not code -- both BSD-3-Clause):
DerAndereJohannes/pyamica's AmicaICA.fit(raw, picks="eeg") /
.apply(raw), and snesmaeili/amica's [mne] extra.