IRI to URI Conversion

Summary

Implement conversion between IRI and URI formats.

Requirements

• toUri() - Convert IRI to URI (percent-encode non-ASCII)
• toIri() - Convert URI to IRI (decode when safe)
• Handle Punycode for domain names
• Preserve semantic equivalence

Example

// IRI with Japanese characters
const iri = try uri.parse("https://example.com/パス");
const uri_str = try iri.toUri(allocator);
// Result: "https://example.com/%E3%83%91%E3%82%B9"

Acceptance Criteria

• Round-trip conversion preserves meaning
• Proper UTF-8 encoding/decoding
• Tests with various scripts (CJK, Arabic, etc.)