Upgrade to tokio 0.3 (#1839)

## Description

This PR updates Lighthouse to tokio 0.3. It includes a number of dependency updates and some structural changes as to how we create and spawn tasks.

This also brings with it a number of various improvements:

- Discv5 update
- Libp2p update
- Fix for recompilation issues
- Improved UPnP port mapping handling
- Futures dependency update
- Log downgrade to traces for rejecting peers when we've reached our max



Co-authored-by: blacktemplar <blacktemplar@a1.net>

common/hashset_delay/Cargo.toml

@@ -5,8 +5,8 @@ authors = ["Sigma Prime <contact@sigmaprime.io>"]
 edition = "2018"
 
 [dependencies]
-futures = "0.3.5"
-tokio = { version = "0.2.22", features = ["time"] }
+futures = "0.3.7"
+tokio-util = { version = "0.4.0", features = ["time"] }
 
 [dev-dependencies]
-tokio = { version = "0.2.22", features = ["time", "rt-threaded", "macros"] }
+tokio = { version = "0.3.2", features = ["time", "rt-multi-thread", "macros"] }

common/hashset_delay/src/hashset_delay.rs

@@ -12,7 +12,7 @@ use std::{
     task::{Context, Poll},
     time::{Duration, Instant},
 };
-use tokio::time::delay_queue::{self, DelayQueue};
+use tokio_util::time::delay_queue::{self, DelayQueue};
 
 pub struct HashSetDelay<K>
 where