Support roxmltree 0.21.1 with updated lifetime parameters and iterator API

[Copilot]

Updates roxmltree from 0.15.0 to 0.21.1, addressing breaking API changes in the XML parsing layer.

Key Changes

• Lifetime parameters: Attribute now requires two lifetimes <'a, 'input> instead of one
• Iterator API: Node::attributes() returns an iterator instead of a slice—now collected into Vec for repeated lookups
• Return types: attribute_of() returns &'a str (from Attribute::value()) instead of &'input str

Test Fixes

Corrected malformed XML closing tags in port.rs tests (<Port> → </Port>), exposed by stricter validation in roxmltree 0.17.0+.

Before/After

// Before (0.15.0)
struct Attributes<'a, 'input> {
    attrs: &'a [roxmltree::Attribute<'input>],
}

// After (0.21.1)  
struct Attributes<'a, 'input> {
    attrs: Vec<roxmltree::Attribute<'a, 'input>>,
}

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