feat: ECDSA functionality with key generation, signing, and verification

Add ECDSA cryptographic functionality to the crypto module, enabling
keypair generation, message signing, and signature verification. This
includes handling Elliptic Curve operations, random key generation, and
finite field arithmetic.

- Introduce `ECDSA` struct for managing the curve, generator, and order.
- Implement methods for generating keypairs, signing messages, and
  verifying signatures.
- Add tests for keypair generation, signing, and signature verification,
  including an invalid signature test.
- Integrate logging for better tracing of ECDSA operations.
- Update dependencies in `Cargo.toml` to include `rand`, `log`, and
  `env_logger` for randomness and logging support.

This change introduces a secure elliptic curve-based signature scheme,
which can be used for authentication and integrity checks in
cryptographic protocols.

Cargo.toml

@@ -10,4 +10,7 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-num-bigint = "0.4.6"
+num-bigint = { version = "0.4", features = ["rand"] }
+rand = "0.8"
+log = "0.4"
+env_logger = "0.10"