Add IRNR (Impuesto sobre la Renta de no Residentes) to Spain's regime

[methodofaction]

es: added IRNR (Impuesto sobre la Renta de no Residentes) retained tax category for income obtained without permanent establishment in Spain. Specific tax rates are not included.

Pre-Review Checklist

• [-] Opened this PR as a draft
• Read the CONTRIBUTING.md guide.
• Performed a self-review of my code.
• [-] Added thorough tests with at least 90% code coverage.
• [-] Modified or created example GOBL documents to show my changes in use, if appropriate.
• [-] Added links to the source of the changes in tax regimes or addons, either structured or in the comments.
• Run go generate . to ensure that the Schemas and Regime data are up to date.
• Reviewed and fixed all linter warnings.
• [-] Been obsessive with pointer nil checks to avoid panics.
• Updated the CHANGELOG.md with an overview of my changes.
• Marked this PR as ready for review.

And if you are part of the org:

• Requested a review from Copilot and fixed or dismissed (with a reason) all the feedback raised.
• Requested a review from @samlown.

[mintlify]

Docs PR opened: invopop/gobl.docs#53

Added the IRNR non-residents income tax category to the Spain regime page, including its scope and regulatory reference.

[mintlify]

Docs PR opened: invopop/docs.invopop.com#389

Added an IRNR entry to the Spain compliance page describing the new non-residents income tax retained category and its scope.

[Copilot]

Pull request overview

Adds a new Spanish retained tax category for IRNR (Impuesto sobre la Renta de no Residentes) intended to represent withholding on non-resident income obtained in Spain without a permanent establishment.

Changes:

• Adds an IRNR retained tax category entry to Spain’s regime data (data/regimes/es.json).
• Updates CHANGELOG.md to document the new category.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
data/regimes/es.json	Adds the new IRNR category metadata (name/title/description) and marks it as retained.
CHANGELOG.md	Documents the addition of IRNR under “Added”.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.49%. Comparing base (ff019e9) to head (750373a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #831   +/-   ##
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  Coverage   93.49%   93.49%           
=======================================
  Files         369      369           
  Lines       20226    20226           
=======================================
  Hits        18911    18911           
  Misses        877      877           
  Partials      438      438           

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