deprecate empty list as indicator for marking all channels

[drammock]

PR Description

paves the way for future change in behavior of mark_channels(..., ch_names=[]) from marking all channels to marking no channels.

Closes #1294

Merge checklist

Maintainer, please confirm the following before merging.
If applicable:

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

[sappelhoff]

clean and great, thanks @drammock

[sappelhoff]

Most of the test failures are flukes, see:

• https://github.com/bids-standard/bids-validator/issues/2124

However, these ones are real:

• https://github.com/mne-tools/mne-bids/actions/runs/10948765960/job/30400543539?pr=1307#step:20:612

could you address them before we merge this, please?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.46%. Comparing base (1cbcfdd) to head (a8034fc).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1307   +/-   ##
=======================================
  Coverage   97.45%   97.46%           
=======================================
  Files          40       40           
  Lines        8777     8781    +4     
=======================================
+ Hits         8554     8558    +4     
  Misses        223      223           

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[drammock]

ok @sappelhoff, looks like all CIs are happy now

[hoechenberger]

Great stuff, thanks @drammock

[sappelhoff]

thanks!