bun: `Bun.serve` does not support streaming responses

`wrapRequestHandler` in `packages/bun/src/integrations/bunserver.ts:189` uses `startSpan`, which ends the span as soon as the handler returns. Deno (`streamResponse`) and Cloudflare (`classifyResponseStreaming` plus a `TransformStream`) both keep the span open until the body finishes.

An SSE or LLM streaming route on Bun reports a span duration covering only the handler, not the stream. This is the common shape for AI apps, which are a large part of the Bun audience.

**Work item.** Move `classifyResponseStreaming` into `@sentry/core` or `@sentry/server-utils` (see D10) and adopt it in `bunserver.ts` with `startSpanManual`.

Start in packages/bun/src/integrations/bunserver.ts:189 at wrapRequestHandler and compare the Deno streamResponse and Cloudflare classifyResponseStreaming plus TransformStream implementations. Review the D10 proposal for placing classifyResponseStreaming, then verify with a streaming response that the span remains open until the body finishes rather than ending when the handler returns.

Written by the indexing model from the issue text.