feat: make chunk size user defined

[joshuef]

BEAKING CHANGE: all APIs updated to have min/max_encryptrable bytes passed in by the user.

This allows for varying the use of the lib.

[maqi]

Just a general question that, to miniumn the impact of the change, why not make CHUNK_SIZE configurable via env ?
something like :

lazy_static! {
    static ref MAX_CHUNK_SIZE: usize = std::env::var("MAX_CHUNK_SIZE")
            .unwrap_or("1048576".to_string())
            .parse::<usize>()
            .unwrap_or(1048576);
}

with that, the change can then be non breaking and be totally backward compatible.

On calling side, there will be no need to change any production code, just a setup configuration for each devnet.

[b-zee]

make CHUNK_SIZE configurable via env

Good idea, but it's possible to use without lazy_static! with std::option_env! (https://doc.rust-lang.org/std/macro.option_env.html)

[maqi]

Good idea, but it's possible to use without lazy_static! with std::option_env!

lazy_static! is still required to construct only once during run time ?

meanwhile, I do agree using std::option_env will be better to avoid pollution during run_time env

[joshuef]

Okay as suggested, closing in favor of: #389