Add unit test for salted WAMP-CRA authentication

[oberstet]

Feature Description

currently, unit test coverage for WAMP authentication in https://github.com/crossbario/crossbar/blob/master/src/crossbar/router/test/test_authorize.py lacks salted WAMP CRA.

this PR #2122 had added test_authextra_wampcra_with_salt(), but was never merged, and by today isn't going to merge again current source tree anymore since the massive reorgs done in modernization of packaging, eg it should be ported to https://github.com/crossbario/crossbar/tree/v25.12.1 and completed

Checklist

• I have searched existing issues to avoid duplicates
• I have described the problem clearly
• I have provided use cases
• I have considered alternatives
• I have assessed impact and breaking changes