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/.gitignore b/.gitignore
index 58e2582..76d9e50 100644
--- a/.gitignore
+++ b/.gitignore
@@ -288,6 +288,7 @@
 /lib/rs/test/src/midlayer.rs
 /lib/rs/test/src/recursive.rs
 /lib/rs/test/src/ultimate.rs
+/lib/rs/test/src/identifiers.rs
 /lib/rs/*.iml
 /lib/rs/**/*.iml
 /lib/swift/.build