chore(examples): fix broken scripts, remove dead ones, add README

[karkikamal098]

Summary

Part of #677 (examples folder rationalization).

• icra2021.py, mexican-wave.py: update to the current ET/Robot/xplot/iscollided API.
• Remove fetch_vision.py (FetchCamera was removed in fix(models): remove FetchCamera, unshippable and unused in RVC3 #545), ikine_evaluate2.py (ikine_min no longer exists, see fix(examples,dhrobot): repair broken ikine_LMS/ikine_min example references #650) and test.py (scratch file).
• Add examples/README.md listing every script with the extras it needs.

Not done here, for your call: merging near-duplicate scripts (RRMC/RRMC_swift, park/baur, mmc/swift_recording), and holistic_mm_non_holonomic.py, which needs a Frankie model with a mobile base to run again.

Related issue

Part of #677.

Checklist

• PR title follows Conventional Commits
• Tests pass locally: no library code changed; all examples/*.py compile
• Added/updated tests: not applicable, examples are not under test
• Type hints / docstrings: no library code changed
• PR is small and focused
• No project-specific test or data files added

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (79b169c) to head (ce92469).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #700   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        143     143           
  Lines      14115   14115           
=====================================
  Misses     14115   14115           

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[petercorke]

Thank you for your interest in RTB -- nice bit of housekeeping. Confirmed icra2021.py was actually broken, not just stale (ETS as ET has no tz/Rz classmethods, so it would have raised AttributeError at that line), and that FetchCamera/ikine_min are genuinely gone from the two removed scripts. The README is a solid addition. Merging as part of #677.