Diesel session store support

[thor314]

I noticed a discussion in tower-sessions between the maintainer of this repo and a contributor intending to add support for Diesel, which seems to have stalled at the end of last year.

I'd like to have support for Diesel, so am proposing to create a pull request with the relevant parts, if that would be welcome.

Please let me know if there's anything I might like to take into consideration.

[maxcountryman]

We don't vendor session stores so please publish this as an independent crate.

There's a number of examples listed in the docs and README which you might reference.

[thor314]

Leaving a note here for others to find regarding diesel.

I spent about 2 hours looking into writing my own session store and evaluated it as not worth it, and will be migrating my project to sqlx instead, which seems generally better supported both by tower-sessions and other ecosystem projects I'm relying on (shuttle).

It was mentioned to me elsewhere that Diesel's has been losing support relative to sqlx/seaORM on the basis of one or more of:

• slow compilation times
• inconsistent async support
• slower developer experience than just writing compile-time checked SQL
• a necessarily complex trait ecosystem creating friction for open source maintainers to support diesel