Function canonicalize_query 

pub fn canonicalize_query(input: &str) -> Result<String, AshError>

Canonicalize a URL query string according to ASH specification.

Canonicalization Rules (9 MUST rules)

1. MUST parse query string after ? (or use full string if no ?)
2. MUST split on & to get key=value pairs
3. MUST handle keys without values (treat as empty string)
4. MUST percent-decode all keys and values
5. MUST apply Unicode NFC normalization
6. MUST sort pairs by key lexicographically (byte order)
7. MUST preserve order of duplicate keys
8. MUST re-encode with uppercase hex (%XX)
9. MUST join with & separator

Example

use ash_core::canonicalize_query;

let input = "z=3&a=1&b=hello%20world";
let output = canonicalize_query(input).unwrap();
assert_eq!(output, "a=1&b=hello%20world&z=3");

// With leading ?
let input2 = "?z=3&a=1";
let output2 = canonicalize_query(input2).unwrap();
assert_eq!(output2, "a=1&z=3");