Clippy 1.49.0 updates and dht persistence test fix (#2156)

## Issue Addressed

`test_dht_persistence` failing

## Proposed Changes

Bind `NetworkService::start` to an underscore prefixed variable rather than `_`.  `_` was causing it to be dropped immediately

This was failing 5/100 times before this update, but I haven't been able to get it to fail after updating it

Co-authored-by: realbigsean <seananderson33@gmail.com>

common/eth2/src/types.rs

@@ -449,7 +449,7 @@ impl<T: FromStr> TryFrom<String> for QueryVec<T> {
     type Error = String;
 
     fn try_from(string: String) -> Result<Self, Self::Error> {
-        if string == "" {
+        if string.is_empty() {
             return Ok(Self(vec![]));
         }