Support zero-copy deserialization from memfiles

[mratsim]

In some protocol or serialization format, the json to deserialize is embedded in a file (in my case safetensors) along with accompanying data and we know the offset and length of that data.

Currently the library can only process string inputs, this means that we have to copy the data into a string even though we could memory-map the json data and use toOpenArray and a cast to get openArray[char].

Given that in Nim openArray[char] also matches strings, we should be able to change all the parseHook to take openArray[char].

[georgelemon]

Check this collection of tiny parsers: https://github.com/openpeeps/openparser. Currently, JSON and CSV are supported. Zero-copy deserialization via memfiles. API reference: https://openpeeps.github.io/openparser/

Under the hood, the JSON parser is pretty similar to jsony (you still have hooks and all) but also support for scientific notation and JSONL file (newline-delimited). Some unit tests here.