fix: a couple uncaught exceptions during coverage processing

[matt-codecov]

related to codecov/engineering-team#1520

i reviewed all of the uncaught exceptions during report processing. this PR addresses two of the highest-firing ones. others should be addressed but are more work and don't fire as frequently so i am punting on them

the services/report/report_processor.py change addresses a somewhat common uncaught exception: ValueError: invalid literal for int() with base 10: 'ignored'. JSON-ified simplecov reports have "ignored" as a coverage value for skipped lines. we should convert those to -1 which is how the pyreport format represents skipped lines

the services/report/languages/simplecov.py change addresses the dominant uncaught exception during report processing: lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1. the surrounding code is basically blindly attempting to parse it as JSON, and then attempting to parse it as XML, and then returning "it's a text file" if neither passes. so failing to parse it as XML is fine, we just weren't catching all the relevant exceptions. now we are. if these are truly empty files, i think they will no-op and if the overall upload has no non-empty files then we will return a ReportEmptyError and set the appropriate error code.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.99%. Comparing base (ab219bc) to head (90fa2ee).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
services/report/languages/simplecov.py	50.00%	1 Missing ⚠️
services/report/report_processor.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #908      +/-   ##
==========================================
- Coverage   97.99%   97.99%   -0.01%     
==========================================
  Files         446      446              
  Lines       35634    35636       +2     
==========================================
+ Hits        34920    34921       +1     
- Misses        714      715       +1     

Flag	Coverage Δ
integration	41.98% <0.00%> (-0.01%)	⬇️
unit	90.84% <33.33%> (-0.01%)	⬇️

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[codecov-notifications]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
services/report/languages/simplecov.py	50.00%	1 Missing ⚠️
services/report/report_processor.py	0.00%	1 Missing ⚠️

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✅ All tests successful. No failed tests were found.

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[Swatinem]

For the eager json/xml parsing, we should maybe check that the contents start/end with {} or [] in case of json, or <> in case of xml.

I contemplated adding such a check before attempting a real parse, just to notice that we have a test that begins with a BOM which you can’t easily strip.

Maybe stripping trailing whitespace and then just checking that the file ends with ]} for json or > for xml would also work. Might be worth thinking about as a followup.