Parse Vietnamese dates with zero-padded months (#1297)

[gaoflow]

Fixes #1297.

Vietnamese dates with a zero-padded month such as 21 tháng 09 năm 2025 were not parsed as absolute dates. The vi locale data only listed the un-padded month forms (tháng 9), so tháng 09 did not match a month name and fell through to the generic tháng -> month token, yielding a wrong relative date:

import dateparser
dateparser.parse("21 tháng 09 năm 2025", languages=["vi"])
# -> datetime.datetime(2024, 9, 16, 8, 16, 26)  # garbage, drifts with "now"

dateparser.parse("21 tháng 9 năm 2025", languages=["vi"])  # un-padded works
# -> datetime.datetime(2025, 9, 21, 0, 0)

Fix

Add zero-padded month aliases (tháng 0N and thg 0N) for months 1-9 in the supplementary language data and regenerate vi.py. Months 10-12 already carry their two-digit forms, so they are untouched.

dateparser.parse("21 tháng 09 năm 2025", languages=["vi"])
# -> datetime.datetime(2025, 9, 21, 0, 0)

Tests

Added a test_translation case (tests/test_languages.py): param("vi", "21 tháng 09 năm 2025", "21 september 2025"). It is RED on the unpadded-only data (translates to 21 month 09 2025) and GREEN with the fix. The full tests/test_languages.py suite passes (1366 passed).

Disclosure: I prepared this fix with AI assistance under my direction; I reviewed and verified the change and the test myself.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.11%. Comparing base (08c78d3) to head (291c840).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1338   +/-   ##
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  Coverage   97.11%   97.11%           
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  Files         235      235           
  Lines        2909     2909           
=======================================
  Hits         2825     2825           
  Misses         84       84           

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