Support touchstone file with more than 9 ports.

[MaxJPRey]

Support touchstone file with more than 9 ports.
Previously we were only selecting the last digit to get the number of ports contained in the touchstone file.

Fix #928

[codecov]

Codecov Report

Merging #935 (d093ec1) into main (5389252) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #935      +/-   ##
==========================================
- Coverage   80.21%   80.21%   -0.01%     
==========================================
  Files         128      128              
  Lines       37419    37419              
==========================================
- Hits        30015    30014       -1     
- Misses       7404     7405       +1     

[jhillairet]

If not done before in the code, I would suggest to lower() the touchstone_full_path somewhere, as one can often sees Touchstone files with using upper cases extentions such as : '.S2P'

[MaxJPRey]

If not done before in the code, I would suggest to lower() the touchstone_full_path somewhere, as one can often sees Touchstone files with using upper cases extentions such as : '.S2P'

Great suggestion @jhillairet . It is done. Thanks.

[maxcapodi78]

LGTM