Bug Fix: Correct Intra-Site Travel

[RHammond2]

This PR fixes a bug where ServiceEquipment.crew_transfer() was changing the location from a specific system to the site when a crew was transferred back to the servicing equipment causing the intra-site travel to be from None to a system instead of from a system to another system with regards to distance traveled.

[codecov[bot]]

Codecov Report

Merging #84 (d830351) into develop (d3acd76) will increase coverage by 0.36%. The diff coverage is 30.55%.

@@             Coverage Diff             @@
##           develop      #84      +/-   ##
===========================================
+ Coverage    55.98%   56.35%   +0.36%     
===========================================
  Files           21       21              
  Lines         3281     3267      -14     
  Branches       619      614       -5     
===========================================
+ Hits          1837     1841       +4     
+ Misses        1352     1336      -16     
+ Partials        92       90       -2     

Impacted Files	Coverage Δ
wombat/core/mixins.py	64.70% <ø> (ø)
wombat/core/port.py	17.85% <0.00%> (+0.73%)	:arrow_up:
wombat/core/simulation_api.py	50.92% <0.00%> (ø)
wombat/core/repair_management.py	76.25% <37.50%> (+2.63%)	:arrow_up:
wombat/core/service_equipment.py	63.70% <83.33%> (+0.93%)	:arrow_up:

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