remove chainspec from the beacon api client

[benluelo]

this is super annoying to deal with. we should instead have "unbounded" versions of all of the types, with a way to convert to the "bounded" version where needed. something like this:

let block = beacon_api_client.block().await;
let mainnet_block: Block<Mainnet> = block.try_into().unwrap();

the only time the chainspec matters is when doing consensus verification. having it be part of the beacon client itself makes the client practically useless for other usecases (a prime example is hubble).

this will likely involve creating new "unbounded" versions of all types with a <C: ...> generic parameter, either through a proc macro or manually (probably manually).

• todo: how to name these types?

[benluelo]

this was included in #2661