196 escaped quote in arg string

// PINS: an escaped quote inside a string argument is DATA — an argument
// scanner must not treat `\"` as a closing quote. THREE scanners had this
// bug, each spelled differently, and each was found by a different program:
//
//   - lexer.parseArgs tracked strings with no backslash handling at all, so
//     `\"` flipped in_string off and every comma in the quoted text split the
//     arg list;
//   - flow_parser.findTopLevelParen spelled the skip as a bare `continue`,
//     which does not skip the escaped char;
//   - lexer.indexOfAtDepthZero — the COLON scanner that decides `name: value`
//     — spelled it as `continue` inside a `for (text, 0..)`, where skipping a
//     byte is not even expressible. Its comment claimed the skip the loop
//     shape forbids.
//
// The three cases below are separate programs to the compiler and the same
// program to their author, which is why fixing two of them left the third.
//
//   1. commas inside escaped quotes, plus a second argument that must
//      survive the split (kopium's request body — a JSON string full of \"
//      and prose commas, koru-examples/kopium/c_chat_pane.k);
//   2. an ODD number of escaped quotes ahead of a colon INSIDE the string.
//      Parity is the whole trigger: with an even count the broken tracker
//      lands back inside the string by accident and the colon is skipped
//      correctly, which is why case 1 passed for months while this failed.
//      Here the string's own `:` was read as an argument label, splitting
//      `print.ln`'s one Expression into a name and a value;
//   3. the same shape with an interpolation after the colon, which is what a
//      program emitting JSON actually writes (the ECS benchmark entry,
//      tests/benchmarks/003_ecs_reactive).

~import std/io

~pub tor first { msg: string, tail: string } -> string

~proc first|zig {
    _ = tail;
    return msg;
}

~first(msg: "one \"two, three\" four", tail: "unsplit"): out |> std/io:print.ln("{{ out:s }}")

~std/io:print.ln("\",\"n\": three escaped quotes and a colon")

~std/io:print.ln("{\"scenario\":\"dense\",\"frames\":{{ 100:d }}}")