feat: add mvs-putty

[zachcp]

Description

Add putty implementation to the TS and Py MolViewSpec libraries

Followed the same argument structure as other representations:

MVS type	Mol* sizeTheme used	What size_factor actually controls
cartoon	uniform	value = size_factor → constant tube radius
backbone	uniform	value = size_factor → constant tube radius
ball_and_stick	uniform	value = size_factor → constant atom/bond size
line	uniform	value = size_factor → constant line width
spacefill	physical	scale = size_factor → scales vdW radii
carbohydrate	uniform	value = size_factor → constant symbol size
surface (molecular)	physical	scale = size_factor → scales vdW-based surface
surface (gaussian)	physical	scale = size_factor → scales vdW-based surface
putty	uniform | uncertainty	sizeFactor is either a constant scale or scales the — the per-residue B-factor .

Note: The current MVS template implementations both use embedded Molstar within their output widgets and the current molstar MVS implementation doesn't yet support putty. We will want to hold off on this PR until the Molstar implementation is in place and we have a public release that supports putty.

Actions

• Added description of changes to the [Unreleased] section of CHANGELOG.md
• When adding new features:
  • Added example(s) to app/api/examples.py
  • Added Jupyter Notebook to test-data/notebooks (python) and test-data/notebooks-ts (typescsript) with new features
  • Added MkDocs documentation in docs
  • When changing the API, make sure the change is coherent between the TS and Python versions (see molviewspec-ts/readme.md).