Revert ed25519 identities back to secp256k1 for lean client

[unnawut]

Describe the feature

leanEthereum/leanSpec#8 (comment)

Additional context

No response

[syjn99]

ream/crates/networking/p2p/src/network/lean/mod.rs

Line 106 in 320a3ce

let local_key = Keypair::generate_secp256k1();

We're currently using secp256k1, so I think this issue can be closed.

[unnawut]

Ah ok I think I was mistaken with reading libp2p’s code