Add `std::encoding::url` module

[mjm918]

Summary

Add URL encoding/decoding (percent-encoding) support as part of the std::encoding module.

Parent issue: #48

Functions

Function	Signature	Description
encode	(s: string) -> string	URL-encode a string
decode	(s: string) -> string throws DecodeError	URL-decode a string

Usage

use std::encoding::url::*;

var safe: string = encode("hello world & more");  // "hello%20world%20%26%20more"
var original: string = decode(safe);

// With error handling  
var text: string = decode("%ZZ") catch e {
    println(e.message);
    return;
} ?? "";

Implementation Notes

• Encode all characters except unreserved characters (A-Z, a-z, 0-9, -, _, ., ~)
• Use Rust's percent-encoding or urlencoding crate
• Handle UTF-8 sequences properly

Exception

exception DecodeError {
    position: int,
}

[mjm918]

Implemented in std/naml-std-encoding/src/url.rs with encode/decode functions and unit tests.