THRIFT-5306: Rust code and generated code no longer has clippy warnings (Rust 1.40)

Client: rs

NOTE: Also properly update the min/max supported Rust versions
diff --git a/lib/rs/src/protocol/multiplexed.rs b/lib/rs/src/protocol/multiplexed.rs
index 9c3ba7c..83498fb 100644
--- a/lib/rs/src/protocol/multiplexed.rs
+++ b/lib/rs/src/protocol/multiplexed.rs
@@ -203,7 +203,7 @@
         let ident = TMessageIdentifier::new("bar", TMessageType::Call, 2);
         assert_success!(o_prot.write_message_begin(&ident));
 
-        #[cfg_attr(rustfmt, rustfmt::skip)]
+        #[rustfmt::skip]
         let expected: [u8; 19] = [
             0x80,
             0x01, /* protocol identifier */