Ignore quotes when detecting the row separator

[gaoflow]

:auto row-separator detection scans the sample for the first CR/LF without tracking quote state, so a CR inside a quoted field is mistaken for the row separator. CSV therefore cannot parse its own generate output whenever a field contains \r:

CSV.parse(CSV.generate {|c| c << ["a\rb", "x"]})
# => [["a\rb", "x\n"]]   # wrong: the \n was swallowed into the last field
CSV.parse(CSV.generate {|c| c << ["a\r\nb", "x"]})
# => CSV::MalformedCSVError: Unquoted fields do not allow new line
CSV.parse(CSV.generate {|c| c << ["\r"]})
# => CSV::MalformedCSVError: Any value after quoted field isn't allowed

All three parse correctly with an explicit row_sep: "\n", which isolates the fault to :auto detection. detect_row_separator now skips CR/LF that fall inside a quoted field. An unquoted CR is still honored as a separator, so old Mac line endings keep working, and explicit row_sep paths are untouched.

Added round-trip and detection tests in test/csv/parse/test_row_separator.rb; the full suite stays green (527 tests, 4050 assertions). This is distinct from #107, which is about an explicit non-standard row_sep.

[kou]

• Could you rename unquoted_index to find_unquouted_string_index or something? I feel that no verb method name is strange for this because the receiver is Parser not String.
• Could you rename sample to text or string because sample is strange in this context?