Remove Python 2.7: Simple syntax and import cleanups

[AadarshM07]

Summary

This PR removes Python 2.7 compatibility code across the codebase, replacing deprecated io.open() calls with the built-in open() function, removing __future__ imports, dropping Python 2-only shims (such as nonzero and urllib2 fallbacks), and simplifying file I/O helpers.

References

Closes #13883

Reviewer guidance

Location of Changes:

1. build_tools/i18n/fonts.py
2. build_tools/i18n/utils.py
3. docker/entrypoint.py
4. kolibri/core/analytics/test/test_utils.py
5. kolibri/core/auth/constants/facility_presets.py
6. kolibri/core/content/management/commands/generate_schema.py
7. kolibri/core/content/test/test_channel_import.py
8. kolibri/core/content/utils/paths.py
9. kolibri/core/content/utils/stopwords.py
10. kolibri/core/deviceadmin/utils.py
11. kolibri/core/logger/management/commands/generateuserdata.py
12. kolibri/core/sqlite/utils.py
13. kolibri/core/utils/nothing.py
14. kolibri/core/webpack/hooks.py
15. kolibri/plugins/qti_viewer/kolibri_plugin.py
16. kolibri/utils/i18n.py
17. kolibri/utils/pskolibri/common.py

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.19.0b2.dev0_git.67.g01c22069.pex
Windows Installer (EXE)	kolibri-0.19.0b2.dev0+git.67.g01c22069-windows-setup-unsigned.exe
Debian Package	kolibri_0.19.0b2.dev0+git.67.g01c22069-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.19.0b2.dev0+git.67.g01c22069.dmg
Android Package (APK)	kolibri-0.19.0b2.dev0+git.67.g01c22069-0.1.6-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.19.0b2.dev0+git.67.g01c22069.zip
TAR file	kolibri-0.19.0b2.dev0+git.67.g01c22069.tar.gz
WHL file	kolibri-0.19.0b2.dev0+git.67.g01c22069-py2.py3-none-any.whl