Optimize input parsing

- Use handrolled "parsing" instead of CSV

lib/planet_express/shipments/shipment_reader.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'csv'
-
 module PlanetExpress
   class ShipmentReader
     include Enumerable
@@ -13,7 +11,9 @@ module PlanetExpress
     end
 
     def each
-      CSV.new(input, headers: false, col_sep: ' ').each do |row|
+      input.each_line do |line|
+        row = line.split(" ")
+
         date = parse_date(row)
         shipping_option = find_shipping_option(row)