Update usage of `*babyjub.PublicKey` to `babyjub.PublicKeyComp`
- when the key is not defined, internally is used `babyjub.EmptyBJJComp`, which is a `[32]byte` of zeroes of type `babyjub.PublicKeyComp`
- the API continues returning `nil` when the key is not defined

- In SQL Tables, set rollup_vars.forge_l1_timeout to BIGINT (instead of BYTEA)
- In "bigint" encoding/decoding used with meddler, store the *big.Int as raw
  bytes, instead of base64 to be more space efficient