[Flight] Walk parsed JSON instead of using reviver for parsing RSC payload

[AbanoubGhadban]

Background

Backport of facebook/react#35776 — ~75% speedup in RSC chunk deserialization.

The react-server-dom-webpack package currently uses JSON.parse(json, reviver) to deserialize RSC payloads. The reviver callback is a major bottleneck: V8's JSON.parse is implemented in C++, and invoking a JS reviver callback for every key-value pair incurs ~4x overhead even with a no-op reviver.

Proposed change

Replace JSON.parse(json, reviver) with a two-step approach:

1. JSON.parse(json) — runs entirely in V8's C++ engine, no callbacks
2. reviveModel() — recursive pure-JS walk that applies RSC transformations

This needs to be applied across all runtime environments (browser, edge, Node.js).

Benchmark results (from upstream PR)

Payload	Speedup
Small (142B)	+72%
Medium (914B)	+73%
Large (16.7KB)	+75%
XL (25.7KB)	+76%
Table (1000 rows, 110KB)	+78%

Implementation approach

Rebuild react-server-dom-webpack from React fork rsc-patches/v19.0.3 with the optimization applied (fork PR).

Acceptance criteria

• RSC payload parsing works correctly
• Nested Suspense boundaries work
• Client/server component mix works
• Deserialization benchmarked on a real app