feat: expose obtaining reference to Mnemonic from DirectSecp256k1HdWallet (#6083)

* feat: expose obtaining reference to Mnemonic from DirectSecp256k1HdWallet

* updated getters for stringified mnemonic

common/client-libs/validator-client/src/signing/direct_wallet.rs

@@ -10,7 +10,7 @@ use cosmrs::tx;
 use cosmrs::tx::SignDoc;
 use nym_config::defaults;
 use thiserror::Error;
-use zeroize::{Zeroize, ZeroizeOnDrop};
+use zeroize::{Zeroize, ZeroizeOnDrop, Zeroizing};
 
 type Secp256k1Keypair = (SigningKey, PublicKey);
 
@@ -128,9 +128,20 @@ impl DirectSecp256k1HdWallet {
         Ok(accounts)
     }
 
+    pub fn secret(&self) -> &bip39::Mnemonic {
+        &self.secret
+    }
+
+    #[deprecated(
+        note = "use either .secret() for obtaining &bip39::Mnemonic or .mnemonic_string() for Zeroizing wrapper around the String"
+    )]
     pub fn mnemonic(&self) -> String {
         self.secret.to_string()
     }
+
+    pub fn mnemonic_string(&self) -> Zeroizing<String> {
+        Zeroizing::new(self.secret.to_string())
+    }
 }
 
 #[must_use]