Add a pure, no-I/O RFC 4180 CSV reader and writer to the Commons project
(greenfield — no CSV code existed).
CsvParser: string / TextReader -> rows of string[]; streaming IEnumerable
overload + eager Parse(string) + thin ParseWithHeader. Handles quoted
fields (embedded delimiter/CR/LF/CRLF, "" -> " escape), space
preservation, CRLF/LF/CR terminators, no phantom trailing row. Strict
malformed-input policy: FormatException with 1-based line/column on a
quote inside an unquoted field, a char after a closing quote, or an
unterminated quote. Faithful empty-line policy: a blank line is one empty
field (callers filter).
CsvWriter: rows -> string / TextWriter; quote-on-demand (delimiter, quote,
CR, LF only; internal quotes doubled), configurable delimiter/newline
(default CRLF), optional quote-all, no trailing terminator.
Tests (xUnit + Shouldly, 109): full RFC edge corpus for the parser, the
writer quote-on-demand rules, and the required Parse(Write(rows)) == rows
round-trip property over a table of every tricky character (x CRLF/LF/
quote-all/semicolon).
Claude-Session: https://claude.ai/code/session_01LVneM3eh1UtJxEisFXgmox
Joseph Doherty
17c7e97efb