fix(encryption): rename os_random to random_seed and fix ESK derivation in tests

Rename os_random field to random_seed per review feedback. Fix tests
that constructed SharedSecretKey with a hardcoded EphemeralSecretKey
instead of deriving it via EphemeralSecretKey::new.

integration_tests/tests/auth_transfer/private.rs

@@ -710,7 +710,7 @@ async fn ppt_cant_chain_call_faucet() -> Result<()> {
             InputAccountIdentity::Public,
             InputAccountIdentity::PrivatePdaInit {
                 vpk,
-                os_random: [0; 32],
+                random_seed: [0; 32],
                 npk,
                 identifier: 1337,
                 seed: None,