add example for comparing subscriptions from different providers

[0xlosh]

Closes: https://github.com/alloy-rs/examples/issues/146

added new_heads to compare, simply run cargo run --example new_heads -- -r reth:ws://localhost:8546 -r alchemy:xxx -r other_provider:other_url -r ... to start

[0xlosh]

tysm, this looks pretty good, only have some nits

will edit tmw and add pending_txs too, im not sure what gakonst meant when he mentioned to test eth_getBlock against other providers too, what exactly is there to compare?

[0xlosh]

cargo run --example new_heads -- -r reth:ws://localhost:8546 -r alchemy:wss://eth-mainnet.g.alchemy.com/v2/<api_key>

cargo run --example pending_txs -- -r reth:ws://localhost:8546 -r alchemy:wss://eth-mainnet.g.alchemy.com/v2/<api_key>

unfortunately i dont have a local geth node running along to test that too, feel free to edit the code

[0xlosh]

@mattsse thanks got it, but im running my own reth node actually