Public output for ZkProgram

[mitschabaude]

closes #523
bindings companion: o1-labs/o1js-bindings#4

• adapt the Pickles interface in snarky.d.ts to take both public input + output, instead of just input, to follow the changes in Public output for ZkProgram o1js-bindings#4
• propagate these changes to the Proof class, which is now Proof<PublicInput, PublicOutput>
• also propagate the changes to the ZkProgram API
• do not change SmartContract, which has the public output fixed to undefined

testing:

• check that updating the Pickles spec from Input to Input_and_output with an empty output type doesn't break verification of zkapp proofs on the current network https://berkeley.minaexplorer.com/transaction/5Jv4brtooog2XxCoYqXwYDBqF39gzjQXKAc3t1234sQC5TEQQGDx

docs:

• changelog (in Clean up previous proof arguments handling in Pickles/SnarkyJS #876)
• update recursion docs

[Trivo25]

this is great!