Apply namespace deduplication to xsl:namespace-alias branches

[Copilot]

The namespace deduplication logic (using isNamespaceDeclaredOnAncestor) was only applied to the non-alias branch, causing nested literal result elements with xsl:namespace-alias to repeat namespace declarations on every element.

Changes

• Applied isNamespaceDeclaredOnAncestor check to both aliasPrefix === '#default' and prefixed alias branches
• Ensures consistent deduplication behavior across alias and non-alias namespace handling

// Before: unconditional xmlns attribute
if (aliasPrefix === '#default') {
    if (namespaceUri) {
        domSetAttribute(newNode, 'xmlns', namespaceUri);
    }
}

// After: deduplicated against ancestors
if (aliasPrefix === '#default') {
    if (namespaceUri && !this.isNamespaceDeclaredOnAncestor(output, 'xmlns', namespaceUri)) {
        domSetAttribute(newNode, 'xmlns', namespaceUri);
    }
}

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