Fix memory leaks in ext/sodium on failure of some functions

Infallible in practice right now, but should be fixed as infallible today does not mean infallible tomorrow:
- sodium_crypto_s

Fix memory leaks in ext/sodium on failure of some functions

Infallible in practice right now, but should be fixed as infallible today does not mean infallible tomorrow:
- sodium_crypto_sign_publickey_from_secretkey
- sodium_crypto_kx_seed_keypair
- sodium_crypto_kx_keypair
- sodium_crypto_auth
- sodium_crypto_sign_ed25519_sk_to_curve25519
- sodium_pad

Fallible today:
- sodium_crypto_sign_ed25519_pk_to_curve25519

Closes GH-14309.

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