Handling top and bottom GC routing

[mdecea]

Modifies route_fiber_array to be able to handle simple situations were there are ports at the top and bottom.

Before this PR, we would have situations like this:

With the PR, such a situation is solved (when using optical_routing_type=0:

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 71.85%. Comparing base (4a66ed9) to head (33a1cac).

Files	Patch %	Lines
gdsfactory/routing/route_fiber_array.py	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2560      +/-   ##
==========================================
- Coverage   71.86%   71.85%   -0.01%     
==========================================
  Files         367      367              
  Lines       23814    23816       +2     
  Branches     3929     3930       +1     
==========================================
  Hits        17114    17114              
- Misses       5501     5502       +1     
- Partials     1199     1200       +1     

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