facet-xml-diff 0.43.1

Diff-aware XML serialization—render structural diffs as readable XML.

## Overview

This crate renders diffs between facet values as XML with visual diff markers.
It shows what changed between two values in a format that's easy to read,
with proper alignment, colored output, and collapsing of unchanged regions.

## Example

```rust
use facet::Facet;
use facet_diff::tree_diff;

#[derive(Facet)]
struct Rect {
    fill: String,
    x: i32,
    y: i32,
}

let old = Rect { fill: "red".into(), x: 10, y: 20 };
let new = Rect { fill: "blue".into(), x: 10, y: 20 };

let xml = facet_xml_diff::diff_to_string(&old, &new)?;
```

Output:

```xml
<rect
← fill="red"
→ fill="blue"
  x="10" y="20"
/>
```

## Features

- **Diff markers**: `←`/`→` (or `-`/`+`) prefix lines to show old vs new values
- **Value-only coloring**: Only the changed values are colored, not the whole line
- **Alignment**: Attributes align properly for readability
- **Collapsing**: Long runs of unchanged content are collapsed with `...`
- **ANSI colors**: Optional terminal colors for better visibility

## Options

```rust
use facet_xml_diff::{DiffSerializeOptions, DiffSymbols, DiffTheme};

let options = DiffSerializeOptions {
    symbols: DiffSymbols::ascii(),  // Use -/+ instead of arrows
    theme: DiffTheme::default(),
    colors: true,
    indent: "  ",
    max_line_width: 80,
    collapse_threshold: 3,
    ..Default::default()
};
```

## Use Cases

- Debugging configuration changes
- Displaying diffs in CLI tools
- Generating human-readable change logs
- Testing serialization by comparing expected vs actual output