Add HRV RQA regression tests

[Aman-Tripathi27]

Summary

• add deterministic coverage for valid HRV RQA input and output schema
• verify custom dimension, delay, and tolerance parameters affect the recurrence rate
• verify short input returns the expected validation error

Testing

• MPLCONFIGDIR=/private/tmp/neurokit-matplotlib python3 -m pytest -o addopts="" tests/tests_hrv.py -k hrv_rqa -q

Result: 3 passed.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.26%. Comparing base (ff419d9) to head (41b3f73).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1206      +/-   ##
==========================================
+ Coverage   57.78%   58.26%   +0.48%     
==========================================
  Files         310      310              
  Lines       15680    15680              
==========================================
+ Hits         9060     9136      +76     
+ Misses       6620     6544      -76     

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