chore: fix some clippy warnings

This commit fixes clippy warning `useless_conversion`.

Also, a false positive rule `literal_string_with_formatting_args` is
introduced in the nightly toolchain, we cannot `allow` it because it
is a new rule that does not exist in the stable toolchain, so we
should ignore it manually.

Ref: rust-lang/rust-clippy#13928

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>

volo-grpc/src/layer/loadbalance/mod.rs

@@ -97,7 +97,7 @@ where
                 .await
                 .map_err(|err| err.into())?,
             _ => {
-                return self.service.call(cx, req).await.map_err(Into::into);
+                return self.service.call(cx, req).await;
             }
         };
 

volo-thrift/src/client/layer/timeout.rs

@@ -25,7 +25,7 @@ where
             Some(duration) => {
                 let start = std::time::Instant::now();
                 match tokio::time::timeout(duration, self.inner.call(cx, req)).await {
-                    Ok(r) => r.map_err(Into::into),
+                    Ok(r) => r,
                     Err(_) => {
                         let msg = format!(
                             "[VOLO] thrift rpc call timeout, rpcinfo: {:?}, elpased: {:?}, \
@@ -43,7 +43,7 @@ where
                     }
                 }
             }
-            None => self.inner.call(cx, req).await.map_err(Into::into),
+            None => self.inner.call(cx, req).await,
         }
     }
 }

volo-thrift/src/transport/pool/make_transport.rs

@@ -54,6 +54,6 @@ where
 
     async fn call(&self, kv: (K, Ver)) -> Result<Self::Response, Self::Error> {
         let mt = self.inner.clone();
-        self.pool.get(kv.0, kv.1, mt).await.map_err(Into::into)
+        self.pool.get(kv.0, kv.1, mt).await
     }
 }