Rust MSRV jump

[kevinhartman]

Hi there, and thanks a lot of this neat library!

I don't know that this makes sense as an "issue", but the latest minor version (0.10.0) jumps the Rust MSRV from 1.65 to 1.83. As I'm sure you're aware, any crates depending on 0.10.0 will now need to update their MSRV to 1.83. I was hoping to use this crate in Qiskit for our instruction representation, but we cannot raise our MSRV to 1.83 yet (we are currently at 1.70, and discussing a bump to 1.79). That said, we don't strictly need 0.10.0, but we tend to be somewhat conservative, so I hesitate to add a dependency on bitfield-struct if we will need to aggressively update our own MSRV to pick up bugfixes etc.

These stats recently came to my attention, which seem helpful when planning bumps.
https://lib.rs/stats#rustc

Feel free to close this whenever!

[wrenger]

The jump was motivated by the new support for const mut references in 1.83. I have been waiting for this for a long time.
Still, I understand the need for backwards compatibility. I have to find out if this could be enabled conditionally based on the compiler version. If that is the case, I could lower the version requirement again...

[wrenger]

I've been planning for a long time to use const_mut_refs to make some internal changes (#7).

I'll maintain the 0.9 branch for the foreseeable future, and have backported your PR #59 to version 0.9.4. Any changes and fixes that are compatible will also be backported.

Sorry that my answer took so long. Last week was just too busy.