Add Plant N Demand and N Limiting

[Alomir]

Summary

• Motivation: Why is this change needed?
• What: Short description of the functional or documentation changes

How to test

Steps to reproduce and verify the change locally:

make
cd tests/smoke/<new-or-updated-test> ../../sipnet -i sipnet.in

Related issues

• Fixes # (or "Relates to #N" if this is not a resolution of that ticket)

Checklist

• Tests added for new features
• Documentation updated (if applicable)
• docs/CHANGELOG.md updated with noteworthy changes
• Code formatted with clang-format (run git clang-format if needed)
• Requested review from at least one CODEOWNER

For model structure changes:

• Removed \fraktur font formatting from docs/model-structure.md for implemented features