feat: Feature/json dump proper

[Zakir032002]

Summary

Add Redis-compatible DUMP/RESTORE support for JSON type using type coercion approach.

Maps JSON objects to Redis String type (RDBTypeString) during serialization, preserving data while maintaining full Redis compatibility. Similar to how SortedInt coerces to Set.

Closes #3319

Changes

Implementation Approach

• SaveObjectType(): Maps kRedisJson → RDBTypeString
• SaveObject(): Retrieves JSON via json_db.Get(), dumps to string, saves via SaveStringObject()
• No custom RDB type: Uses standard Redis String encoding for full compatibility

Trade-offs

• ✅ Redis Compatible: Any Redis instance can RESTORE the payload
• ✅ Simple Implementation: Reuses existing String serialization
• ✅ Data Preserved: JSON content fully preserved as string
• ⚠️ Type Changes: After RESTORE, type becomes string (not ReJSON-RL)
• ⚠️ Requires Re-import: Need JSON.SET to restore JSON functionality

This matches the pattern used for SortedInt (which becomes Set after RESTORE).

Testing

Manual Testing

127.0.0.1:6666> JSON.SET mykey $ '{"name":"Alice","age":30}'
OK

127.0.0.1:6666> TYPE mykey
ReJSON-RL

127.0.0.1:6666> DUMP mykey
"\x00\x19{\"age\":30,\"name\":\"Alice\"}\x06\x00 \xe8\x8f\xe8\xa4\x1a\xa5N"

127.0.0.1:6666> RESTORE newkey 0 "\x00\x19{\"age\":30,\"name\":\"Alice\"}\x06\x00 \xe8\x8f\xe8\xa4\x1a\xa5N"
OK

127.0.0.1:6666> TYPE newkey
string  # Type coerced to string

127.0.0.1:6666> GET newkey
"{\"age\":30,\"name\":\"Alice\"}"  # Data preserved

[PragmaTwice]

The format design in this PR is not compatible with Redis at all. Not even close. Please ensure that you understand the design and the code.

[Zakir032002]

@PragmaTwice , Thank you for pointing this out, I will take this as learning and will do a proper implementation

[Zakir032002]

From next time for these types can i just combine 2-3 type in a pr?