ENH: Add TimeChange behaviour to plot_evoked

[Gnefil]

Reference issue (if any)

Implements #14024.

What does this implement/fix?

Adds TimeChange behaviour in mne.viz.plot_evoked(), which is the underlying function for mne.Evoked.plot() too.

Additional information

[Copilot]

Pull request overview

This PR adds TimeChange UI-event integration to mne.viz.plot_evoked() (and therefore Evoked.plot()), enabling evoked plots to both publish time changes on click and react to externally-published time changes by updating a vertical time marker.

Changes:

• Publish TimeChange events from evoked butterfly plots on mouse click.
• Subscribe evoked plots to time_change events and move/update a vertical selection marker accordingly.
• Add/extend tests to cover click-driven time selection and TimeChange event handling.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
mne/viz/evoked.py	Publishes and subscribes to TimeChange events; adds time-marker updates in evoked plots.
mne/viz/tests/test_evoked.py	Adds tests ensuring click selection creates a marker and TimeChange updates it.

[wmvanvliet]

It works, but the current UI feels a little brittle, with selecting a channel or selecting a time range also moving the time cursor. Would it be possible to have the following behavior?

1. Hovering the mouse over empty space in the axis draws a "shadow" cursor, like you implemented in plot_evoked_topo.
2. Hovering the mouse over a curve makes that curve a little thicker and shows the channel label (changing what is the current on-click behavior to a hover behavior).
3. Clicking without dragging anywhere in the axis places the time cursor and emits a TimeChange event
4. Clicking-and-dragging anywhere in the axis selects a span and draws a topomap (current behavior unchanged)

[Gnefil]

It works, but the current UI feels a little brittle, with selecting a channel or selecting a time range also moving the time cursor. Would it be possible to have the following behavior?

1. Hovering the mouse over empty space in the axis draws a "shadow" cursor, like you implemented in plot_evoked_topo.
2. Hovering the mouse over a curve makes that curve a little thicker and shows the channel label (changing what is the current on-click behavior to a hover behavior).
3. Clicking without dragging anywhere in the axis places the time cursor and emits a TimeChange event
4. Clicking-and-dragging anywhere in the axis selects a span and draws a topomap (current behavior unchanged)

No problem, I will look into them.