Port Python test to Elixir: `25-beginswith-test`

[ninetteadhikari]

Overview

Note: This PR is dependent on this base PR to be merged.

This work is done according to "Milestone 3. Convert Python test suite to eunit or exunit" as stated in the Scope of Work with Sovereign Tech Agency Resilience Program.

This PR includes:

• Port 25-beginswith-test.py test to Elixir
• Remove corresponding python test

Testing recommendations

Run:

make elixir or make elixir tests=test/elixir/test/mango/25-beginswith-test.exs

Related Issues or Pull Requests

Checklist

• [ ] Code is written and works correctly
• [ ] Changes are covered by tests
• [ ] Any new configurable parameters are documented in rel/overlay/etc/default.ini
• [ ] Documentation changes were made in the src/docs folder
• [ ] Documentation changes were backported (separated PR) to affected branches