fix(examples): point 06-sse at a live public SSE endpoint

[donbagger]

The example's own comment says "httpbin doesn't host an SSE endpoint, so this uses sse.dev which echoes a message every 2s", but sse.dev no longer resolves (NXDOMAIN), so the example dies on the initial GET. This swaps in DexPaprika's free, keyless price stream and filters on the named token_price event, which also exercises the SseEvent.event field properly; the manual AbortController became AbortSignal.timeout per the runtime-baseline rule in AGENTS.md. Verified live with pnpm dlx tsx examples/06-sse.ts (plus pnpm lint, pnpm typecheck, and the full vitest suite, 932 passing), first event off the wire:

event: token_price
data: {"address":"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2","chain":"ethereum","price":"1840.545532633754","timestamp":1784283722,...}

Disclosure: I do DevRel for DexPaprika. The endpoint is public, no key or signup needed.

[donbagger]

Small one from July. sse.dev is gone at the DNS level, NXDOMAIN today, so examples/06-sse.ts cannot run for anyone who copies it out of the repo.

The patch swaps it for a public keyless SSE stream and skips the keepalive events so the example still exits after three messages. I checked the replacement endpoint again today and it is still emitting events.