CSV transformer for Selecto query results.

Converts query results to CSV format with configurable options:

• Headers: Include/exclude column headers
• Delimiter: Custom field separators (comma, tab, semicolon, etc.)
• Quoting: Proper escaping for special characters
• Null handling: Custom null value representation
• Streaming: Efficient processing for large datasets

Options

• :headers - Include headers (default: true)
• :delimiter - Field separator (default: ",")
• :quote_char - Quote character (default: """)
• :null_value - Null representation (default: "")
• :force_quotes - Quote all fields (default: false)
• :line_ending - Line ending style (default: "\n")

Examples

iex> Selecto.Output.Transformers.CSV.transform(
...>   [["Alice", 25], ["Bob", 30]],
...>   ["name", "age"],
...>   ["name", "age"]
...> )
{:ok, "name,age\nAlice,25\nBob,30\n"}

iex> Selecto.Output.Transformers.CSV.transform(
...>   [["John, Jr.", nil]],
...>   ["full_name", "age"],
...>   ["full_name", "age"],
...>   delimiter: ";", null_value: "N/A"
...> )
{:ok, "full_name;age\n\"John, Jr.\";N/A\n"}