fix: escape carriage return as 
 in builder output

[gaoflow]

The builder emits a raw carriage return in text and attribute values. A raw CR is normalized to LF by any conforming XML parser (XML 1.0 §2.11), so the CR is silently lost on the next parse — including through fast-xml-parser's own round trip:

const b = new XMLBuilder();
const p = new XMLParser({ htmlEntities: true });
p.parse(b.build({ n: "A\rB" })).n;   // "A\nB", not "A\rB"

Fix: add CR to the default entity table so it serializes as 
, which is how CR has to be represented in XML. LF and TAB are left verbatim — they survive a round trip; CR is the only character that gets folded.

A sweep of U+0001–U+00FF in both text and attribute positions confirms CR is the only value that fails the round trip. The added tests cover the escaped output, the round trip, and that LF/TAB stay unescaped.