Support passwords for encrypted SSL client keys

[skhe]

Summary

• Pass ssl_pwd from the Python DPI interface through the Go connector to TLS.
• Decrypt traditional encrypted PEM client keys; reject missing or wrong passwords and unsupported encrypted PKCS#8 keys explicitly.
• Keep UKey unsupported rather than silently opening a different connection.

Verification

• Local ARM macOS Python 3.10 against SSL-enabled DM8: all five SSL tests passed, including an encrypted RSA client key with a password containing +, &, and a space.
• Ordinary DM8: ssl_pwd without ssl_path rejected as expected.
• Go TLS security tests, Go bridge tests, patch consistency check, Python 3.9 syntax compilation, and git diff --check passed.

Encrypted PKCS#8 private keys remain unsupported and are reported clearly.