Add Romanian (RO) tax regime

[teodor2002]

• The official documentation (ANAF) regarding VAT rates can be found at:

  • ANAF - Cod fiscal 227/2015 (VAT rates)
  • Legea nr. 141/2025 - VAT 19% → 21%

• The official documentation regarding the RO algorithm can be found at:

  • RO Identity Implementation, page 76

• The output of the test command go test --update ./... can be found at examples/ro/out

• All tests have been passed, including the mage check

• Code is clear containing comments and guidelines

[codecov]

Codecov Report

❌ Patch coverage is 95.55556% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.73%. Comparing base (458d352) to head (6ee3378).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
regimes/ro/tax_identity.go	89.18%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #898   +/-   ##
=======================================
  Coverage   94.73%   94.73%           
=======================================
  Files         316      318    +2     
  Lines       17198    17288   +90     
=======================================
+ Hits        16292    16378   +86     
- Misses        560      562    +2     
- Partials      346      348    +2     

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