Broaden the TextReader pull cursor toward libxml2's xmlTextReader:
- Attribute nodes: moveToFirstAttribute/moveToNextAttribute/
moveToAttribute(_:)/moveToElement reposition the cursor onto each
attribute as an .attribute node and back.
- Namespace accessors: namespaceURI, localName, prefix from the current
element's or attribute's resolved name.
- xml:lang: inherited down the tree, overridable per element, reset when
it goes out of scope.
- Position: lineNumber/columnNumber report where each node begins, so a
streaming consumer can locate findings in the source. EventReader now
records each node's start mark.
DOCTYPE and entity-reference nodes are not surfaced (the DTD is exposed
through documentType, and entities are expanded inline); whitespace is
not split into significant/insignificant (needs the content model);
baseURI needs a document URI. The accurate positioning path for editor
findings remains readTree with source ranges.
Closes#98
