Describe the feature

Add a new example demonstrating how to implement custom hardforks for a chain built on Reth

TODO

• define custom hardforks (enum, trait, and configuration)
• integrate hardforks into EVM configuration to enable feature gating

Additional context

https://github.com/alloy-rs/hardforks/blob/6dd26f64e8d21228aac9ee6830074e026bcfe4d1/crates/op-hardforks/src/lib.rs#L24-L31

and

https://github.com/berachain/bera-reth/blob/4b8f9af4ee8f250143266e104cde04b504e5941c/src/hardforks/mod.rs