Parquet iterator does not take groupname key word

[chto]

Problem & Solution Description (including issue #)

Hi,
Parquet iterator does not take the groupname keyword, so it will crash.
This pull request fixes it.

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.84%. Comparing base (9596d74) to head (fe7dbf6).

Files with missing lines	Patch %	Lines
src/rail/core/stage.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #246      +/-   ##
==========================================
- Coverage   99.86%   99.84%   -0.03%     
==========================================
  Files          54       54              
  Lines        3746     3753       +7     
==========================================
+ Hits         3741     3747       +6     
- Misses          5        6       +1     

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[eacharles]

Could you clean this up a bit, remove the swap file and print statement.