fix(node-http): handle undefined headers in request

[gwitwer]

Summary

• Normalizes request.headers to an empty object before passing to handleAuthorization
• Fixes TypeError: Cannot convert undefined or null to object when client.request() is called without a headers option

Root Cause

The handleAuthorization function in interceptors.ts calls Object.entries(request.headers) without checking if headers is defined. When users call:

await client.request({ method: "GET", url: "..." });

...without specifying headers, request.headers is undefined, causing the error.

Test plan

• Run node-http example without headers: await client.request({ method: "GET", url: "..." })
• Verify requests with headers still work: await client.request({ method: "GET", url: "...", headers: {} })

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