Remove bc dependency from Debian package build

[wayyoungboy]

Summary

• replace the Debian package build Python version comparison that used bc -l
• use the candidate Python interpreter itself to verify Python 3.11+
• confirm there are no remaining direct bc command dependencies in check tasks or package scripts

Fixes #232

Verification

• bash -n ubuntu/build_ubuntu.sh
• rg -n "\|\s*bc\b|\bbc\s+-l\b|command -v bc|/usr/bin/bc" . --glob "!*.pyc" --glob "!__pycache__/**" --glob "!dependencies/**" returns no matches
• git diff --check