Add IRNR tax category to Spain regime

[methodofaction]

Summary

• Adds the IRNR (Impuesto sobre la Renta de no Residentes) tax category to the Spanish regime as a retained tax with full i18n name/title and an English description covering scope and rate applicability.
• No fixed rates are defined — applicable percentages depend on income type and recipient residency, so they are supplied per invoice.
• Regenerated data/regimes/es.json and added a CHANGELOG entry.

Test plan

• mage test
• mage lint
• mage generate produces the expected IRNR block in data/regimes/es.json

[mintlify]

Docs PR opened: invopop/docs.invopop.com#390

Added the IRNR non-resident income tax category to the Spain compliance page's special tax types list, noting that rates are supplied per invoice.

[mintlify]

Docs PR opened: invopop/gobl.docs#54

Added the IRNR tax category to the Spain regime page, including overview mention, table entry, and a section explaining scope and per-invoice rates.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.50%. Comparing base (ff019e9) to head (9532b02).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
+ Coverage   93.49%   93.50%   +0.01%     
==========================================
  Files         369      369              
  Lines       20226    20259      +33     
==========================================
+ Hits        18911    18944      +33     
  Misses        877      877              
  Partials      438      438              

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[samlown]

Normally a good idea to add an example or tests, but no worries.