Migrate parsing of unencrypted PKCS#8 private keys to Rust

[alex]

No description provided.

[alex]

paramiko failures are due to paramiko/paramiko#2490 (probably)

[alex]

test cases needed to coverage:

• pkcs8 envelope with invalid version
• pkcs8 envelope with unknown OID
• pkcs8 envelope with EC key where the inner params don't match the outer params
• PKCS#1 EC key with missing params
• EC key (either format) where public key isn't serialization
• PKCS#1 DSA key with invalid version
• PKCS#1 RSA key with invalid version
• PKSC#1 RSA key that's multi-prime
• EC key (with version) with invalid version
• EC key with inner and outer params that do match

[Tarnum-tst]

@alex , could You please make this code (81-86) compatible with Rust 1.63? let...else is unstable in 1.63... :-(

[alex]

We've had an MSRV of 1.65 since cryptography 43.0.0 in July of last year, we're not going to revert that absent exceptional circumstances

[Tarnum-tst]

@alex , I still maintain my custom build based on Rust 1.63 w/o GATs, maturin & workspace deps. It works fast on my retro systems (Win'7 and earlier) and very stable, too. :-)
Replacement:

            let dek_info = match p.headers().get("DEK-Info") {
                Some(dek_info) => dek_info,
                None => {
                    todo!()
                },
            };
            let (cipher_algorithm, iv) = match dek_info.split_once(',') {
                Some((cipher_algorithm, iv)) => (cipher_algorithm, iv),
                None => {
                    todo!()
                },
            };

[alex]

We're not going out of our way to to support things that we don't support.

[alex]

Test cases we need:

• Encrypted PKCS#8, PBES2 with 3DES-CBC
• Encrypted PKCS#8, PBES2 with unknown encryption algorithm
• Encrypted PKCS#8, PBES2 PBKDF2 with unknown PRF algorithm
• Encrypted PKCS#8, PBES2 with unknown KDF
• Encrypted PEM with no DEK-Info
• Encrypted PEM with DEK-Info that doesn't have two, comma separated components
• Encrypted PEM with DEK-Info where the IV isn't valid hex
• Unit tests for hex_decode