Derive Keystore public key from secret key

[MegaRedHand]

Context: #1013

Currently we're parsing it from the file, but the value could be wrong. Also, deriving it from the secret enables us to add an additional check by comparing both the parsed and derived values.

[guha-rahul]

Can i take it?

[MegaRedHand]

Sure! Go ahead! Let me know if you need some pointers.

[guha-rahul]

Sure! Go ahead! Let me know if you need some pointers.
Hey sorry for the late reply but dump as many pointers as you like .

[MegaRedHand]

• The keystore is in lib/keystore.ex.
• We currently parse the public key here:
  

  lambda_ethereum_consensus/lib/keystore.ex

  Lines 26 to 27 in 24acec6

  	# TODO: derive from privkey and validate with this pubkey
  	pubkey = Map.fetch!(decoded_json, "pubkey") |> parse_binary!()

• The idea is to derive the key from the secret key and compare them.
• You might need to add a function to lib/bls.ex for that (keep in mind it's a NIF, so actual code is in Rust and lives inside native/bls_nif)