Add derived variable lapserate

[axel-lauer]

Description

This PR introduces a new derived variable lapserate, the vertical temperature gradient calculated as -dT/dz in K per km.

Checklist

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• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.46%. Comparing base (1ee7ae6) to head (737d19c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2872   +/-   ##
=======================================
  Coverage   95.46%   95.46%           
=======================================
  Files         260      261    +1     
  Lines       15519    15534   +15     
=======================================
+ Hits        14815    14830   +15     
  Misses        704      704           

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