Add RDC compression rollout controls (#97247)
## Summary
Warn during prerendering when the exact UTF-8 size of the uncompressed
postponed-state body exceeds `experimental.maxPostponedStateSize` while
Resume Data Cache compression is enabled.
Add `experimental.disableResumeDataCacheCompression` as an opt-in
rollout flag. It defaults to `false`, preserving the existing compressed
representation. When enabled, both persistence and parsing use raw JSON,
allowing a controlled minimal-mode rollout without format negotiation.
RDC serialization now happens in explicit steps: stringify, check the
raw body size, then conditionally deflate. This avoids compression-ratio
estimates and duplicate serialization.
This is the lower PR in a two-PR stack. It can land first so the raw
representation can be enabled selectively for minimal-mode deployments
and observed on canary before compression is removed.
## Verification
- `pnpm exec jest
packages/next/src/server/resume-data-cache/resume-data-cache.test.ts
packages/next/src/server/app-render/postponed-state.test.ts --runInBand`
- `pnpm --filter=next types`
- `pnpm --filter=next build`
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