[Chronik] Update Rust version to 1.72.0 and nightly to 2023-08-23

Summary:
This allows us to use some of the more recent features in Rust, like OnceCell and OnceLock, and also closes some minor security vulnerabilities.

To update on your local dev instance, you can run the following:

rustup update
rustup install nightly-2023-08-23
rustup component add rustfmt --toolchain nightly-2023-08-23
rustup toolchain link abc-nightly "$(rustc +nightly-2023-08-23 --print sysroot)"
rustup toolchain uninstall nightly-2023-02-17

Test Plan: ./install-dependencies-bullseye.sh, or the update instructions in the summary

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D14410