Building the mutable TreeNode tree from a parsed value Node ran append for every
child. append -> insert detaches the child from any previous parent, rejects a
self/ancestor cycle, and inserts into a children array that grows element by
element. The children the conversion passes come from element.children.map and
are freshly built and parentless, so all three guards are no-ops and the
incremental growth rebuilds an array that was already prepared.
TreeNode.init(adopting:) adopts the prepared array directly and wires each
child's parent. The tree is identical: the same children in the same order with
the same parent links. The adopting initializer is used only by the value-Node
conversion; every public factory keeps the detaching, cycle-checking append path
for externally supplied children that may already live in a tree.
Measured parse ~12% faster on the 20k-item generated corpus via a same-state
A/B (7.7x to ~6.5x slower than libxml2). Verified by TreeNodeAdoptingInitTests
(parent-wiring and post-adoption mutability), the W3C XML conformance corpora,
the Xalan XSLT gold-output corpus, the full suite, the WASM build, and an
adversarial equivalence review.
Add PureXML.Model.TreeNode, a reference-type document tree that knows its
parent and siblings. Navigation goes up and sideways (parent, nextSibling,
previousSibling, ancestors, root, elementChildren, stringValue) and editing
is in place (append, insert before/after, removeFromParent, replace, copy).
Children are held strongly and the parent weakly; attaching a node detaches
it from any prior parent and a node can never become its own ancestor.
parseTree builds one from XML; TreeNode.node converts back for serialization.
Closes#31
