Follow up to persistent tower with tests and API cleaning (#12350) (#12972)

* Follow up to persistent tower

* Ignore for now...

* Hard-code validator identities for easy reasoning

* Add a test for opt. conf violation without tower

* Fix compile with rust < 1.47

* Remove unused method

* More move of assert tweak to the asser pr

* Add comments

* Clean up

* Clean the test addressing various review comments

* Clean up a bit

(cherry picked from commit 54517ea454)

Co-authored-by: Ryo Onodera <ryoqun@gmail.com>

sdk/src/signature.rs

@@ -43,6 +43,15 @@ impl Keypair {
         self.0.to_bytes()
     }
 
+    pub fn from_base58_string(s: &str) -> Self {
+        Self::from_bytes(&bs58::decode(s).into_vec().unwrap()).unwrap()
+    }
+
+    pub fn to_base58_string(&self) -> String {
+        // Remove .iter() once we're rust 1.47+
+        bs58::encode(&self.0.to_bytes().iter()).into_string()
+    }
+
     pub fn secret(&self) -> &ed25519_dalek::SecretKey {
         &self.0.secret
     }