2.5 --> 2.6: backwards incompatible change in #parse method for IOString #106

If you call #seek(n) or #read(n) on StringIO object newer version of CSV.parse ignores current offset position in IO object.

Consider this examples
Ruby 2.5.5

require 'csv'
io = StringIO.new("#meta\na,b\n1,2")
io.read(6) # => "#meta\n"
CSV.parse(io) # => [["a", "b"], ["1", "2"]]

Ruby 2.6.3

io = StringIO.new("#meta\na,b\n1,2")
io.read(6) # => "#meta\n"
CSV.parse(io) # => [["#meta"], ["a", "b"], ["1", "2"]] (contains skipped data)

It looks that new logic always rewinds StringIO and there is now way to pass IO with specific offset position anymore.