Use mul in adjoint-Diagonal multiplications

[jishnub]

Following on from #1207 (comment), this specializes mul instead of specializing * and adding internal functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.96%. Comparing base (579b5f7) to head (e74d6d9).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1225      +/-   ##
==========================================
+ Coverage   91.93%   91.96%   +0.03%     
==========================================
  Files          34       34              
  Lines       15384    15380       -4     
==========================================
+ Hits        14143    14144       +1     
+ Misses       1241     1236       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[dkarrasch]

Sorry I didn't ping you, but I think this is included in #1215?

[jishnub]

Oh right