## Why
Exec-server JSON-RPC payloads can contain decimals, exponent notation, and
integers outside the native 64-bit range. Decoding these values should preserve
their original JSON representation without weakening the existing message
complexity limit.
## What changed
- Enable `serde_json` arbitrary-precision number and raw-value support for the
exec-server protocol.
- Decode serde's number and raw-value wrappers in the bounded JSON visitor,
charging nested raw values against the 256K-value limit.
- Select the JSON-RPC envelope variant from its fields after bounded decoding so
arbitrary-precision values survive message deserialization.
## Testing
Add coverage for exact arbitrary-precision number round trips and for enforcing
the value limit inside raw-value wrappers.
GitOrigin-RevId: a6e0a3fba6f88e4e8a6ff414832f078beb2d2a70
jif
7790524d6b