Switch hello-world and vllm to single-shot once livepeer/go-livepeer#3955 lands

[rickstaa]

What

Switch the hello-world and vllm examples from the persistent live-runner path to single-shot, once single-shot payment is decided and implemented in livepeer/go-livepeer#3955.

Why

Both are request/response (batch) apps, but they currently use the persistent path (reserve_session then proxy then stop_runner_session) as a workaround, because single-shot mode has no payment yet. The persistent path bills by held open wall clock time (a 402 at reservation plus a 5s LivePaymentProcessor ticker), which over charges short request/response calls and ties billing to how long the session is held rather than the work done.

Blocked on

livepeer/go-livepeer#3955 (bill payments for single-shot live runner calls). This is purely a workaround-removal once the billing model is chosen and shipped.

Changes when unblocked

• Register the runner with mode="single-shot".
• Call via the paid single-shot path (target /apps/{runner}/app/{path}), dropping reserve_session and stop_runner_session.
• Remove the persistent-path workaround from both example clients.

Acceptance

• hello-world and vllm run as single-shot, paying per the model decided in feat: bill payments for single-shot live runner calls go-livepeer#3955.
• No held open session and no wall clock ticker for these request/response calls.

[rickstaa]

Can be implemented when livepeer/go-livepeer#3975 is merged.