Fix HRV tuple input handling

[Aman-Tripathi27]

Summary

• support raw (peaks, sampling_rate) tuples without accessing missing metadata
• support (signals, info) tuples returned by processing functions
• add regression tests for both tuple input forms

Testing

• python3 -m pytest -o addopts="" tests/tests_hrv.py -k "tuple_input or tuple_metadata_input" -q
• python3 -m pytest -o addopts="" tests/tests_hrv.py -k "not hrv_missing and not hrv_rsa" -q

The focused tuple tests pass. The non-network HRV suite passes (15 tests); the two omitted tests download data at runtime.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.90%. Comparing base (ff419d9) to head (3c5cc11).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1205      +/-   ##
==========================================
+ Coverage   57.78%   57.90%   +0.12%     
==========================================
  Files         310      310              
  Lines       15680    15673       -7     
==========================================
+ Hits         9060     9076      +16     
+ Misses       6620     6597      -23     

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