periods for near2far adjoint

[mochen4]

Supports periodic boundary condition for near2far adjoint. All the essential mechanism is already in place, so only an additional keyword argument is needed in python.

The k vector should be the same for forward and adjoint run. Since the adjoint sources are computed before flipping k, nothing needs to be changed.

[codecov-commenter]

Codecov Report

Merging #2321 (b74852f) into master (038a2e5) will decrease coverage by 1.21%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2321      +/-   ##
==========================================
- Coverage   73.23%   72.01%   -1.22%     
==========================================
  Files          17       17              
  Lines        4931     5031     +100     
==========================================
+ Hits         3611     3623      +12     
- Misses       1320     1408      +88     

Impacted Files	Coverage Δ
python/adjoint/objective.py	92.38% <ø> (ø)
python/visualization.py	36.68% <0.00%> (-4.78%)	⬇️
python/simulation.py	76.81% <0.00%> (-0.05%)	⬇️
python/adjoint/optimization_problem.py	59.48% <0.00%> (+1.53%)	⬆️