Cycle context variables

Noting that documentation for the cycle tag only mentions cycling through lists of strings, and existing integration tests cover cycling through lists of integers, is the behaviour demonstrated by the following example considered a bug?

require 'liquid'

template = Liquid::Template.parse(
  "{% cycle a, b, c %} {% cycle a, b, c %} {% cycle a, b, c %}")

puts(template.render!({"a" => 1, "b" => 2, "c" => 3}))

Output:

1 1 1

Expected Output:

1 2 3

I can see that the cycle tag was changed with this commit to parse cycle arguments as expressions, rather than treating them as strings. It appears that a string representation of objects returned from parse_expression() doesn't make a good context key.

Start with the reproduction in the issue and the cycle coverage in test/integration/tags/standard_tag_test.rb around line 259. Trace how cycle arguments are parsed and used as context keys, then compare the observed and expected outputs. Done means the intended behavior is established and covered by an appropriate regression test.