Session Pool Management

[sbihel]

Hi, this issue is just to say I wrote a session pool management crate based on r2d2: https://github.com/spruceid/r2d2-cryptoki.

I believe it's the right way of handling concurrent requests for service HSMs like cloud-hosted ones, but I thought maybe you'd have an opinion.

On a side note, I added a Zeroize wrapper for pins to ensure users understand how sensitive they are, and unless you think it's unnecessary I will create a PR as it would belong in this crate.

[ionut-arm]

Hey! Thanks for the heads-up, the r2d2 crate does look pretty nice. I'm considering adding some links, perhaps on the README, to crates that have useful "3rd party" functionality. 🤔

In terms of a PR for zeroizing PINs - yes, please, that would be appreciated.