ENH: Add optional channel name overlay to plot_alignment

[aman-coder03]

What does this PR do?

adds an optional show_channel_names parameter to plot_alignment to overlay channel labels at sensor locations in the 3D alignment view.

Why?

this improves interpretability when inspecting sensor alignment, especially for debugging, teaching, and demonstrations. The feature is fully opt-in and does not change default behavior.

Backward compatibility

fully backward compatible (disabled by default).

Tests

visualization tests pass (dataset-dependent tests skipped as expected).

fixes #13502

[drammock]

take a look at other files in this directory, to see how they should be formatted (e.g. no heading, and mention the author and PR number)

[drammock]

Suggested change

	xyz[0],
	xyz[1],
	xyz[2],
	*xyz,

[drammock]

@aman-coder03 please also look at our tutorials or examples that use plot_alignment, find one where it wouldn't be distracting to include the sensor names, and change the tutorial to use this new parameter. That way we can see how it looks in the built documentation

[aman-coder03]

thanks for your suggestion @drammock
I have updated the changes, happy to adjust the example if you prefer a different one.