Add pins in taper_cross_section

[nikosavola]

This PR

• modifies taper_cross_section to add pins if possible
• handles partialed tapers in gdsfactory/add_tapers_cross_section.py to not overwrite given cross_section2 if None

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (ddd5647) 72.64% compared to head (d22399d) 72.63%.

Files	Patch %	Lines
gdsfactory/add_tapers_cross_section.py	20.00%	4 Missing ⚠️
gdsfactory/components/taper_cross_section.py	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2330      +/-   ##
==========================================
- Coverage   72.64%   72.63%   -0.02%     
==========================================
  Files         368      368              
  Lines       23066    23073       +7     
  Branches     3719     3722       +3     
==========================================
+ Hits        16757    16759       +2     
- Misses       5208     5211       +3     
- Partials     1101     1103       +2     

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