URI Builder/Formatter

Summary

Add a URI builder for constructing URIs from components.

Requirements

• Builder struct with fluent API
• setScheme(), setHost(), setPort(), etc.
• Automatic percent-encoding of components
• Validation during construction
• build() returns formatted URI string

Example API

const result = Uri.builder(allocator)
    .scheme("https")
    .host("example.com")
    .port(8080)
    .path("/api/v1/users")
    .query("page", "1")
    .build();

Acceptance Criteria

• Builder creates valid URIs
• Proper encoding applied
• Tests for various combinations