. PostalService available? and item_oversized? method arguments changed:
 . available? accepts an array of Stock::Package#contents
 . item_oversized? accepts a variant
. Logic change in PostalService#item_oversized?
 . The existing logic was incorrect. An Item is oversized if its longest and second-longest sides are greater than the set limits. The older logic used only the first value from an ascending-ordered array of sides. Now it sorts in descending order, and uses the first two values.
. Specs changed for PostalService#compute as the method argument changed in previous commit.
. Specs added for available? and item_oversized? methods

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