Implement encoding to/decoding from DER-encoded secret key document for `ecdsa::SecretKey`.
Implement encoding to/decoding from protobuf format for ECDSA keys.
Bump dependency `p256` from 0.12 to 0.13.
Bump dependency `sec1` from 0.3.0 to 0.7
Related: #3681.
Pull-Request: #3863.
This PR renames some method names that don't follow Rust naming conventions or behave differently from what the name suggests:
- Enforce "try" prefix on all methods that return `Result`.
- Enforce "encode" method name for methods that return encoded bytes.
- Enforce "to_bytes" method name for methods that return raw bytes.
- Enforce "decode" method name for methods that convert encoded key.
- Enforce "from_bytes" method name for methods that convert raw bytes.
Pull-Request: #3775.
