fix: handle dobject import error with helpful error message

[Paroksh1]

Summary

This PR resolves the dobject import error by bundling the dobject module directly into the activity folder. This ensures the activity works properly even in .xo installs that lack Git history or submodules.

Changes Made

• Removed Git submodule setup for dobject
• Moved all dobject code to arithmetic/dobject/
• Removed .gitmodules and cleaned up .git/config
• Updated arithmetic.py to use Python 3 syntax and direct imports
• Removed deprecated cgitb usage
• Confirmed structure works via Python 3 validation

Why This Fix Is Needed

Sugar users typically install .xo bundles, not via Git. This bundling ensures compatibility across installs. Fix also aligns with maintainer feedback to remove the submodule dependency.

Closes #

[chimosky]

Activity bundles are usually distributed without their git history, so using git wouldn't work.

Plus you're also believing that whoever uses the activity and gets that error would check the logs to see why, that's rarely the case.

The submodule also seems to be nonexistent, so I would suggest finding the right submodule and updating it, then testing to see if that fixes the issue.

[Paroksh1]

Hi @chimosky
I've updated the PR by fully removing the dobject submodule and bundling the required code directly into the activity. Python 3 compatibility is ensured, and the activity is now submodule-independent — works for .xo users too. Let me know if anything more is needed. Thanks a lot!