Better late than never, but finally there is an ICRC3 implementation in Rust available!
You can find all the details here:
Introducing bity_ic_icrc3: A Complete ICRC3 Implementation for Internet Computer Developers
dfinity-rust-libraries/src/icrc3 at master · BitySA/dfinity-rust-libraries · GitHub
It is quite easy to integrate with, and what I like mostly - it also implements all the security related features (certificates, throttling mechanism)