Allow for capacities to be determined post init.

[jonathf]

Instead of pre-declaring amount_capacity in init, allow it to be None, and instead verify it after it when the vehicles come in.

[codecov[bot]]

Codecov Report

Merging #55 (ba009da) into main (8c04882) will decrease coverage by 0.0%. The diff coverage is 69.2%.

@@           Coverage Diff           @@
##            main     #55     +/-   ##
=======================================
- Coverage   80.2%   80.1%   -0.1%     
=======================================
  Files         28      28             
  Lines       1304    1315     +11     
  Branches      17      17             
=======================================
+ Hits        1046    1054      +8     
- Misses       249     252      +3     
  Partials       9       9             

Flag	Coverage Δ
binding	70.2% <ø> (ø)
python	91.7% <69.2%> (-0.4%)	:arrow_down:

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