ci: add self hosted arm runner

[braindigitalis]

Changes the CI to use a native arm7 self-hosted runner. This is hosted on a raspberry pi 4B.
The scripts for anyone to do this if needed are available here if anyone else has the desire to set up a similar self-hosted runner which we could use in the future. The self-hosted runner scripts support arm, arm64, amd64.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.