update to 834.5010.X220.A1.xml files to correct LS/LE segments

[manningmattw-progyny]

• updated the pos element errors
• correctly indented the loops/segments/elements
• the LS/LE segments (and all contained) now match the HIPAA 834 5010X220A1 Implementation Standard (from the fixed indentation, pos element fixes, and also usage updates
• added 834_ls_le_ls dataset to pyx12/test/x12testdata.py
• added a new 834 test in pyx12/test/test_x12n_document.py
• added a new XML round‑trip test in pyx12/test/test_xmlx12_simple.py

[manningmattw-progyny]

@azoner This XML change was tested and confirmed to work with all compatible Python versions and requirements listed for pyx12 versions 2.3.3/2.3.4. If it's not too much trouble, a review/confirmation from you on this would be grand, and getting this updated would breathe a little bit of new life into the project. Thank you for all the work you have done to make pyx12 what it is so far!

[azoner]

Thanks for taking a look at this. I'll review these changes against the 834 IG. If you could, a de-identified 834 example using this loop would be helpful. It would be perfect if you could add the test to x12testdata.py.

[manningmattw-progyny]

Sure! I found pyx12/tests/834_ls_le_ls.txt is an applicable test file for this change, so I just added it into the tests and validated that the tests ran successfully. I also saved the generated 999 from that file to the pyx12/tests/ directory for reference.