Affected: npm: @xmldom/xmldom, npm: xmldom

## Summary

Seven recursive traversals in `lib/dom.js` operate without a depth limit. A sufficiently deeply nested DOM tree causes a `RangeError: Maximum call stack size exceeded`, crashing the application.

**Reported operations:** - `Node.prototype.normalize()` — reported by @praveen-kv (email 2026-04-05) and @KarimTantawey (GHSA-fwmp-8wwc-qhv6, via `DOMParser.parseFromString()`) - `XMLSerializer.serializeToString()` — reported by @Jvr2022 (GHSA-2v35-w6hq-6mfw) and @KarimTantawey (GHSA-j2hf-fqwf-rrjf)

**Additionally, discovered in research:** - `Element.getElementsByTagName()` / `getElementsByTagNameNS()` / `getElementsByClassName()` / `getElementById()` - `Node.cloneNode(true)` - `Document.importNode(node, true)` - `node.textContent` (getter) - `Node.isEqualNode(other)`

All seven share the same root cause: pure-JavaScript recursive tree traversal with no depth guard. A single deeply nested document (parsed successfully) triggers any or all of these operations.

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## Details

### Root cause

`lib/dom.js` implements DOM tree traversals as depth-first recursive functions. Each level of element nesting adds one JavaScript call frame. The JS engine's call stack is finite; once exhausted, a `RangeError: Maximum call stack size exceeded` is thrown. This error may not be caught reliably at stack-exhaustion depths because the catch handler itself requires stack frames to execute — especially in async scenarios, where an uncaught `RangeError` inside a callback or promise chain…