Remove dartpy8 bindings

[jslee02]

Remove the unused dartpy8 bindings, their examples/tests, and all tooling knobs now that the new API work is moving back into the primary dart/dartpy trees. This also cleans up CI (CodeQL + pixi tasks), docs, and scripts so nothing references the old targets.

Testing: pixi run lint

---

Before creating a pull request

• Run pixi run test-all to lint, build, and test your changes
• Add unit tests for new functionality
• Document new methods and classes
• Add Python bindings (dartpy) if applicable

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.47%. Comparing base (04cdf8b) to head (4c64de6).
⚠️ Report is 312 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2206   +/-   ##
=======================================
  Coverage   61.47%   61.47%           
=======================================
  Files         350      350           
  Lines       31338    31338           
  Branches     4055     4055           
=======================================
  Hits        19266    19266           
  Misses      12072    12072           

Flag	Coverage Δ
unittests	61.47% <ø> (ø)

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