Add support for SCRAM-SHA-1-PLUS and SCRAM-SHA-256-PLUS

[wneessen]

Extended SMTP tests to include SCRAM-SHA-1-PLUS and SCRAM-SHA-256-PLUS authentication mechanisms. Adjusted the startSMTPServer function to accept a hashing function and modified the server logic to handle TLS channel binding.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.91%. Comparing base (84f5625) to head (711ce2a).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #323      +/-   ##
==========================================
+ Coverage   84.85%   85.91%   +1.06%     
==========================================
  Files          27       27              
  Lines        2350     2350              
==========================================
+ Hits         1994     2019      +25     
+ Misses        228      201      -27     
- Partials      128      130       +2     

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