prost-amino-derive: upgrade dependencies

[tarcieri]

• Removes the (unused) digest v0.7 dependency
• Bumps the proc macro crates to v1.x:
  • proc-macro2 v1
  • quote v1
  • syn v1
• Bumps sha2 dependency to v0.9

Proc macro updates were done largely by copying and pasting the upstream code from prost-derive and adjusting or adding back prost-amino-related tweaks.

[tarcieri]

Sorry for not breaking this into multiple commits/PRs to make it easier to review (I can still do that if you want).

The sha2-related changes are relatively small and self-contained.

The majority of it is churn from Rust attribute names going from single_idents to multi::segmented::paths.

[xla]

Bump, looks like CI got stuck. Can we get this merge?

[tac0turtle]

I believe @Liamsi created a fork.

[liamsi]

I believe @Liamsi created a fork.

Yeah, I wanted to avoid maintaining a fork for various reasons... Will create a separate repo instead (tmrw), cherry-pick changes from @tarcieri and create a release from there! Sorry for the back and forth.