Support short UTC offset timezones

[CodingFeng101]

Summary

Support two-digit UTC offset timezone strings such as +08 and -03 when they are passed through timezone settings. These values are produced by Python's timezone APIs on some systems, but currently raise UnknownTimeZoneError while equivalent forms like UTC+08, +0800, and +08:00 are accepted.

Changes

• Normalize +HH / -HH timezone strings to the existing UTC+HH matching path.
• Add focused regression coverage for positive and negative short UTC offsets.

Validation

• python -m pytest tests/test_short_utc_offsets.py -q -> 2 passed
• Manual smoke check confirmed dateparser.parse(..., settings={"TIMEZONE": "+08"}) and "-03" no longer raise.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.11%. Comparing base (08c78d3) to head (03bda05).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1340   +/-   ##
=======================================
  Coverage   97.11%   97.11%           
=======================================
  Files         235      235           
  Lines        2909     2911    +2     
=======================================
+ Hits         2825     2827    +2     
  Misses         84       84           

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