[jeff-grimes-pplx]

Summary

• Fixes silent truncation of the seconds component in TzinfoParser.parse() when given an ISO 8601 UTC offset with seconds (±HH:MM:SS or ±HHMMSS), which previously matched only ±HH:MM and discarded :SS.
• Extends DateTimeParser._TZ_Z_RE and DateTimeParser._TZ_ZZ_RE to accept optional seconds in Z / ZZ tokens so arrow.get(a.isoformat()) round-trips cleanly for timestamps with sub-minute UTC offsets (such as historical IANA timezones like America/St_Johns or Europe/Amsterdam).
• Adds unit tests in tests/test_parser.py covering TzinfoParser.parse and DateTimeParser.parse_iso.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2224255) to head (2d0c43f).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1405   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           10        10           
  Lines         2315      2315           
  Branches       358       358           
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  Hits          2315      2315           

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