[Rust]: Implement Private and Public keys

[satoshiotomakan]

Is your feature request related to a problem? Please describe.

Transaction signing is the key responsibility of wallet-core. We need to implement the PrivateKey and PublicKey structures to be able to move one of the blockchains from C++ to Rust.

The Private and Public keys implementation is the next step in moving ETH blockchain to Rust.

Describe the solution you'd like

Add and implement PrivateKey and PublicKey structures in Rust.
The list of elliptic curves need to be supported:

• secp256k1 (in particular, used in ETH blockchain)
• nist256p1
• ed25519 and its modifications:
  • ed25519-blake2b-nano
  • curve25519 (in particular, used in Waves blockchain)
  • ed25519-cardano-seed (used in Cardano blockchain)
• Starkex curve (used in Starknet blockchain)

Checklist

• Explore the Rust crates that provides the secp256k1 implementation.
• Explore the Rust crates that provides the nist256p1 implementation.
• Explore the Rust crates that provides the ed25519 implementation.
• Implement PrivateKey and PublicKey high-level structures in Rust
• Export TWPrivateKey and TWPublicKey FFI types
• Add multiple unit and integration tests (Rust->C++, Rust)

Resources

Crates that can help to achieve the signing:

• crypto
• rust-secp256k1 - a wrapper around a C-library
• libsecp256k1 - secp256k1 implementation in pure Rust
• curve25519-dalek - a library providing group operations on the Edwards and Montgomery forms of Curve25519, and on the prime-order Ristretto group.