Investigate methods of reducing code size for Validator Manager contracts

[geoff-vball]

Context and scope
We have been routinely running up against code size limits for validator-manager contracts, with ERC20TokenStakingManager currently only having ~500 bytes of headroom before hitting the cap, and NativeTokenStakingManager having ~1200 bytes of headroom.

This has prevented us from including external getters for state variables, which are necessary to implement proper tooling for the contracts.

Discussion and alternatives
Would externalizing the churn tracker help us save on code size? Externalizing the churn tracker would also help other implementations include it, which would be helpful because it is consensus-critical.