Use Rust implementation `curve25519-dalek` for curve25519 cryptography

[andreypfau]

https://github.com/dalek-cryptography/curve25519-dalek

Example of using rust in kotlin:
https://github.com/ktorio/ktor/tree/main/ktor-client/ktor-client-webrtc/ktor-client-webrtc-rs