Adding possibilty of different bends in 2x2 cutback

[mdecea]

In the 2x2 cutbacks, if we use the same 180 degree bend for both ports we might end up with waveguides too close to each other:

This PR allows to use different bends for each port. This way we can separate the waveguides form each other, for example using a circular and an Euler bend:

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (fa42520) 72.55% compared to head (f45b9e1) 72.55%.

Files	Patch %	Lines
gdsfactory/components/cutback_2x2.py	57.14%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2485      +/-   ##
==========================================
- Coverage   72.55%   72.55%   -0.01%     
==========================================
  Files         366      366              
  Lines       23385    23389       +4     
  Branches     3809     3810       +1     
==========================================
+ Hits        16968    16969       +1     
- Misses       5290     5292       +2     
- Partials     1127     1128       +1     

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[joamatab]

looks great! thank you Marc