doc_tests: run on Python 3.14 and regenerate notebooks

[dhalperi]

Move the doc_tests CI job from Python 3.10 to 3.14 so the notebook
regeneration tests run on the same interpreter as the rest of the
matrix. build_docs and readthedocs_build stay on 3.10 (the latter must
match ReadTheDocs' environment).

Regenerate the checked-in notebooks against current batfish. vxlan_evpn
picks up the renamed evpnL3VniProperties columns
(Import_Route_Target/Export_Route_Target -> plural *_Route_Targets, now
List of str) from batfish/batfish#10117. The remaining notebook diffs
are the newer pandas' HTML output (non-breaking spaces, an added
mathjax_ignore table class) and the kernel version metadata bump, which
match what the 3.14 job now produces.

---

Prompt:

Let's swap github CI to use 3.14 for doc tests, then replace all the
notebooks with the new ones

[batfish-bot]

This change is 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.58%. Comparing base (9ecc844) to head (0bcf8e4).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #990   +/-   ##
=======================================
  Coverage   86.58%   86.58%           
=======================================
  Files          26       26           
  Lines        3906     3906           
  Branches      527      527           
=======================================
  Hits         3382     3382           
  Misses        364      364           
  Partials      160      160           

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[dhalperi]

@dhalperi reviewed 13 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on dhalperi).