Replace json format with more efficient binary file format

[pemistahl]

Currently, the language models are stored as json files. Json is somewhat slow to deserialize. Let's investigate whether there is a more efficient binary file format which can be deserialized faster.

A promising candidate could be the MessagePack or Protobuf format.

[getreu]

What about postcard - Rust?

[xxaier]

why not use https://github.com/apache/arrow-rs

and

this is Rust serialization benchmark

https://github.com/djkoloski/rust_serialization_benchmark

I recommand https://crates.io/crates/speedy