chore: import upstream snapshot with attribution

docs/articles/modules/csv.md

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+## When To Use std.csv
+
+In Zerolang, use `std.csv` for allocation-free CSV validation, record scanning,
+field decoding, and small fixed-arity CSV writers.
+
+Runnable today:
+
+| API | Return | Notes |
+| --- | --- | --- |
+| `std.csv.valid(bytes)` | `Bool` | Validates bounded CSV input with quoted fields and CRLF or LF records. |
+| `std.csv.recordCount(bytes)` | `Maybe<usize>` | Counts valid records, returning null on malformed input. |
+| `std.csv.record(bytes, index)` | `Maybe<Span<u8>>` | Borrows one record slice by ordinal, excluding the line terminator. |
+| `std.csv.fieldCount(record)` | `Maybe<usize>` | Counts fields in one valid record. |
+| `std.csv.field(buffer, record, index)` | `Maybe<Span<u8>>` | Decodes one field into caller storage. |
+| `std.csv.encodedFieldLen(field)` | `usize` | Computes the bytes needed to write one CSV field. |
+| `std.csv.writeField(buffer, field)` | `Maybe<Span<u8>>` | Writes one CSV field with quotes when required. |
+| `std.csv.writeRecord2(buffer, left, right)` | `Maybe<Span<u8>>` | Writes a two-field record ending in `\n`. |
+| `std.csv.writeRecord3(buffer, first, second, third)` | `Maybe<Span<u8>>` | Writes a three-field record ending in `\n`. |
+
+Metadata labels:
+
+- effects: parse
+- allocation behavior: no allocation; decoded fields and writer output use caller storage
+- target support: target-neutral
+- error behavior: `Maybe` helpers return null on malformed input or insufficient storage
+- ownership notes: records borrow from the input; fields and writer output borrow from caller buffers
+- examples: `conformance/native/pass/std-csv.graph`
+
+## Example
+
+```zero
+pub fn main(world: World) -> Void raises {
+    let input: Span<u8> = "name,quote\nAda,\"a,b\"\n"
+    let record: Maybe<Span<u8>> = std.csv.record(input, 1_usize)
+    var field_buf: [16]u8 = [0_u8; 16]
+    var quote: Maybe<Span<u8>> = null
+    if record.has {
+        quote = std.csv.field(field_buf, record.value, 1_usize)
+    }
+    if std.csv.valid(input) && quote.has && std.mem.eql(quote.value, "a,b") {
+        check world.out.write("csv ok\n")
+    }
+}
+```
+
+## Design Notes
+
+CSV helpers follow the common RFC 4180 field rules: comma-separated fields,
+quoted fields, doubled quotes inside quoted fields, and CRLF or LF record
+separators. Quoted fields may contain newlines.
+
+The writer surface is fixed-arity. Use `writeField` when a custom writer loop
+is needed.