Implement ThresholdDecryptionRequest and ThresholdDecryptionResponse

[KPrasch]

Requirements

Implement two new serde-versioned bytes-serializable entities for use in nucypher/nucypher and nucypher/nucypher-ts threshold decryption product (working title "tCBD"). Bob will use these entities to gather threshold decryption shares. Both python and WASM binding are needed.

Entities

• ThresholdDecryptionRequest (ThRq)
  • ritual ID: int
  • ciphertext: ferveo.Ciphertext
  • conditions: Conditions
  • context: Context
• ThresholdDecryptionResponse (ThRs)
  • share: ferveo.DecryptionShare

Notes

• Implementation is very similar to ReencryptionRequest/ReencryptionResponse
• see development mockup here: https://github.com/nucypher/nucypher/blob/385e982e1c0bd830894b63f5a809881d6b412ab4/nucypher/utilities/mock.py
• see usage in nucypher/nucypher's Ursula here: https://github.com/nucypher/nucypher/blob/385e982e1c0bd830894b63f5a809881d6b412ab4/nucypher/network/server.py#L143
• consider encrypting ThresholdDecryptionResponse for Bob.
• will require a version bump