Platform/Framework setup gaps

[lforst]

We currently have gaps in the SDK setup for certain platforms, frameworks, runtimes that we should address:

•  We don't support auto-instrumentation for Bun
• We need a better setup utility for Next.js (like withBraintrust in next.config.ts)
• We need a better story for setups where people cannot pass in a loader hook (Vercel, Netlify, Lambda?)
• We need a better story for deno --preload for auto-instrumentation (first verify whether it works with current hook)

^ This list is a bit WIP