Add support for fNIRS

[rob-luke]

PR Description

This PR replaces #406

This PR adds support for fNIRS. There is a BEP in progress for NIRS support here... bids-standard/bids-specification#802

The BEP is in the final stages. We are writing the manuscript up. The spec has been stable for a long time and is implemented in other software (Homer)

Merge checklist

Maintainer, please confirm the following before merging:

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

[codecov]

Codecov Report

Merging #960 (d14a30b) into main (81bccd6) will not change coverage.
The diff coverage is n/a.

❗ Current head d14a30b differs from pull request most recent head 1f82fb8. Consider uploading reports for the commit 1f82fb8 to get more accurate results

@@           Coverage Diff           @@
##             main     #960   +/-   ##
=======================================
  Coverage   94.52%   94.52%           
=======================================
  Files          25       25           
  Lines        3583     3583           
=======================================
  Hits         3387     3387           
  Misses        196      196           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 81bccd6...1f82fb8. Read the comment docs.

[rob-luke]

Closed in favor of original PR thanks to git magic from larsoner