Handle paid Tempo session SSE fetches

[parvahuja]

Summary

• Added a private client response hook for methods that need to adapt successful paid fetch responses.
• Used that hook for Tempo session SSE responses so payment control events can post top-up and voucher credentials while callers receive the application stream.
• Added focused coverage for the fetch hook and the Tempo session SSE response path.

Why

Paid Tempo session SSE streams can request additional vouchers after the initial paid retry has already returned a 200 event stream. Fetch.from previously returned that stream directly, so callers using payment-aware fetch could receive payment control events without the client posting the required voucher credentials.

Validation

• VITE_TEMPO_NETWORK=none pnpm exec vp test --run src/tempo/session/client/Transports.test.ts
• VITE_TEMPO_NETWORK=none pnpm exec vp test --run src/client/internal/Fetch.test.ts -t "lets methods wrap post-payment responses"
• pnpm check:types
• pnpm check
• git diff --check

[pkg-pr-new]

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commit: c30d9bc