address issue 3162 by applying threshold to CVN position check

[zhexu14]

This PR addresses #3162 by applying a threshold on the CVN position check. In the save game provided in #3162 , the floating point comparison were failing even though the CVN was in (roughly) the same position.

This PR was tested by:

• Loading the save from Mission generation failure "could not find a carrier in the mission matching..." #3162 in the develop branch and observing that mission generation failed
• Loading the same save using this feature branch and observing that the mission generation succeeded.

[codecov]

Codecov Report

Merging #3174 (352d6bf) into develop (2344fc0) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##           develop    #3174   +/-   ##
========================================
  Coverage    45.78%   45.78%           
========================================
  Files          474      474           
  Lines        25793    25793           
  Branches      4515     4515           
========================================
  Hits         11809    11809           
  Misses       13963    13963           
  Partials        21       21           

Files Changed	Coverage Δ
...siongenerator/aircraft/waypoints/recoverytanker.py	30.00% <0.00%> (ø)