improve tf2ss conversion

[baggepinnen]

by using MatrixPencils, which offers possibility of constructing a minimal realization. This option is much faster than the old approach minreal(ss(P)) for large systems

[JuliaControlBot]

This is an automated message.
Plots were compared to references. 1/11 images have changed, see differences below.
After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

Difference	Reference Image	New Image
✔️ 0.006

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.60%. Comparing base (c66b3d1) to head (aba649d).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #971      +/-   ##
==========================================
- Coverage   92.83%   92.60%   -0.23%     
==========================================
  Files          41       41              
  Lines        5007     4973      -34     
==========================================
- Hits         4648     4605      -43     
- Misses        359      368       +9     

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