Taiga: Function privacy

[XuyangSong]

customer: @mariari
performer: @XuyangSong
deadline: null
estimated: null
started: null
actual: null
completed: null
confirmed: null
dependencies:

• Function privacy roadmap
• recursive zkp dependencies
• recursive zkp dependencies PRs
• Poseidon sponge full duplex mode
• Use Poseidon sponge in Halo2 transcript in prover and out-of-circuit verifier
• elaborate the function privacy in spec
• Integrate the function privacy to Taiga, a big refactor(ptx, tx, etc.) needs #149

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