Version 2.16.4

What's Changed

• Fix: make confine spring constant a floating point number by @mlund in #459
• CI use LLVM 20 by @mlund in #460
• More tolerant mass center drift
  Improved tolerance handling for mass center drift calculations. (Commit: Mar 19, 2025)
• Update JSON schema
• Updated schema.yml. (Commit: Mar 12, 2025)
• Added missing constraint: index property to the JSON schema. (Commit: Sep 13, 2025)
• Added primitive model example
  Introduced a new example demonstrating the primitive model. (Commit: Jul 10, 2025)
• Added primitive model notebook
  Added a corresponding Jupyter notebook for the primitive model example. (Commit: Jul 11, 2025)

🐛 Bug Fixes

• Fixed exprtr git hash issue which caused builds to fail

Full Changelog: v2.16.3...v2.16.4