fix(openai): use new Function trick for node: dynamic imports

[OwenMcGirr]

Problem

The template literal import(\node:${name}`)intextToSpeechandtextToSpeechStreaminginsideopenai.tscauses **build failures** in Turbopack (Next.js 16) and Vite. Both bundlers attempt to statically resolve dynamic imports and cannot handle anode:` prefix with a dynamic suffix.

Reproduces as:

Module not found: Can't resolve 'node:' <dynamic no slash>
  const importNodeBuiltin = async (name) => import(`node:${name}`);

Fix

Replace with the new Function pattern already used in abstract-tts.ts, audio-converter.ts, and playht.ts:

// Before
const importNodeBuiltin = async (name: string) => import(`node:${name}`);

// After  
const importNodeBuiltin = (name: string) => new Function('m', 'return import(m)')(name);

Fixes #32