chore: fix dead code warning for 'Sealed' trait and 'sample_floyd2' func (#799)

Author: bp7968h

tower/src/lib.rs

@@ -219,6 +219,7 @@ pub use tower_layer::Layer;
 pub use tower_service::Service;
 
 #[allow(unreachable_pub)]
+#[cfg(any(feature = "balance", feature = "discover", feature = "make"))]
 mod sealed {
     pub trait Sealed<T> {}
 }

tower/src/util/rng.rs

@@ -116,6 +116,7 @@ where
 ///
 /// ref: This was borrowed and modified from the following Rand implementation
 /// https://github.com/rust-random/rand/blob/b73640705d6714509f8ceccc49e8df996fa19f51/src/seq/index.rs#L375-L411
+#[cfg(feature = "balance")]
 pub(crate) fn sample_floyd2<R: Rng>(rng: &mut R, length: u64) -> [u64; 2] {
     debug_assert!(2 <= length);
     let aidx = rng.next_range(0..length - 1);