fix: preserve duplicate response headers

[StopMakingThatBigFace]

📝 Description

Added

• Added Headers.getSetCookie() to return raw Set-Cookie response header values as an array, matching modern Node/undici-style fetch behavior.

const cookies = response.headers.getSetCookie();
// ["session=abc123; Path=/", "csrf=token123; Path=/"]

Fixed

• Fixed duplicate response headers being dropped by the native transport. Response headers are now passed from the native layer as ordered [name, value] tuples instead of a plain object, so repeated headers are preserved.
• response.headers.get(name) now returns comma-joined values for repeated headers, matching fetch behavior.

response.headers.get('x-dupe');
// "one, two"

• response.headers.get('set-cookie') now preserves all received Set-Cookie values in the joined header view, while response.headers.getSetCookie() and response.wreq.setCookies expose the raw cookie header array.
• Response.clone() now preserves duplicate response headers instead of collapsing them through object conversion.

Tests

• Added coverage for repeated response headers, repeated Set-Cookie headers, Headers.getSetCookie(), and cloned responses.

Build & CI

• Limited the test workflow to run only when code, package metadata, Rust sources, scripts, TypeScript config, or the test workflow itself changes.
• Limited the native build workflow on pull requests to run only when native build inputs, package metadata, scripts, or the build workflow itself changes.
• Documentation-only changes such as README.md, docs/**, issue templates, and skill files no longer trigger the test or native build CI workflows.

🎯 Type of Change

• 🐛 Bug fix
• ✨ New feature
• 📚 Documentation update
• 🔧 Build/CI configuration