net/pyrad: Update to 2.4 [1]

While I'm here:

• Switch to GitHub for a while to keep the EXAMPLES option as the useful examples aren't included with the sdist at the moment.

• Make package concurrent safe due to the example files that are installed outside of Python's site-lib directory.

• Convert to option helpers.

• Add "do-test" target to make future QA easier.

PR: 259332
Reported by: Gian-Simon Purkert [1]
Approved by: maintainer timeout (14+ days)
MFH: 2021Q4
Security: 17702e54-3da0-11ec-b7e0-3085a9a95629

(cherry picked from commit 81389bf63ec797a6797a05a10fab6a958a281da5)