[ENH] Define "phenotype" as a data type not nested inside subjects

[effigies]

Closes #1828. Please continue the conversation in that issue, and reserve this PR for discussing concrete changes.

[yarikoptic]

attn @bids-standard/bep036

[ericearl]

Does this mean phenotype/ is permitted, but not required under the subject/[session/] directory? BEP036 is leaning into the aggregated model of tabular phenotypic data file storage at the root-level phenotype/ subdirectory.

[effigies]

To permit it, we would need a file rule where subject and session are optional, so this describes the current situation reasonably well, as it can't be subject- or session- specific.

I do not have a specific objection to permitting it to be used inside subject/session directories, but if BEP036 is not proposing it, it won't happen.

Happy to consider alternative wordings that make this clearer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.55%. Comparing base (fa58763) to head (f5a4863).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2050      +/-   ##
==========================================
+ Coverage   83.49%   83.55%   +0.05%     
==========================================
  Files          17       17              
  Lines        1509     1508       -1     
==========================================
  Hits         1260     1260              
+ Misses        249      248       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.