a idea to enhance simdjson.parse performance

[theweipeng]

hello, I find that the simdjson.parse is very slow. i think if your use napi to create string, nodejs would copy the string bytes. the bestway to create string is use v8's String.substring, which would create a sliceString in v8 that no need copy memory. simdjson can generate a new buffer, and use javascript to constructe the json object via the buffer.