Reduce outbound requests to eth1 endpoints (#2340)

## Issue Addressed

#2282 

## Proposed Changes

Reduce the outbound requests made to eth1 endpoints by caching the results from `eth_chainId` and `net_version`.
Further reduce the overall request count by increasing `auto_update_interval_millis` from `7_000` (7 seconds) to `60_000` (1 minute). 
This will result in a reduction from ~2000 requests per hour to 360 requests per hour (during normal operation). A reduction of 82%.

## Additional Info

If an endpoint fails, its state is dropped from the cache and the `eth_chainId` and `net_version` calls will be made for that endpoint again during the regular update cycle (once per minute) until it is back online.


Co-authored-by: Paul Hauner <paul@paulhauner.com>

common/fallback/src/lib.rs

@@ -2,8 +2,9 @@ use itertools::{join, zip};
 use std::fmt::{Debug, Display};
 use std::future::Future;
 
+#[derive(Clone)]
 pub struct Fallback<T> {
-    servers: Vec<T>,
+    pub servers: Vec<T>,
 }
 
 #[derive(Debug, PartialEq)]