Allows single entries in molecules parameter

[joaomcteixeira]

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Allows specifying single string when only one molecule is given as input. Hence, both cases are allowed:

molecules = ["mol1.pdb"]

or

molecules = "mol1.pdb"

[codecov-commenter]

Codecov Report

Merging #439 (c573fe8) into main (088e998) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #439      +/-   ##
==========================================
+ Coverage   71.14%   71.26%   +0.12%     
==========================================
  Files          92       92              
  Lines        5757     5764       +7     
==========================================
+ Hits         4096     4108      +12     
+ Misses       1661     1656       -5     

Impacted Files	Coverage Δ
src/haddock/gear/prepare_run.py	46.80% <100.00%> (+1.77%)	⬆️
tests/test_gear_prepare_run.py	98.92% <100.00%> (+0.08%)	⬆️

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