feat: Add NoosphereVRF shared singleton for verifiable randomness

[nolnol3]

Add VRF module (src/v1_0_0/vrf/) providing epoch-based Merkle tree random values shared across all consumer dApps on a chain.

• INoosphereVRF.sol: Public interface
• NoosphereVRF.sol: Singleton with epoch management, Merkle proof verification, global request ID counter, and replay prevention
• NoosphereVRFConsumer.sol: Abstract for dApps to inherit, integrates with Noosphere compute pipeline and exposes virtual hooks

[gemini-code-assist]

Summary of Changes

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This pull request integrates a robust Verifiable Random Function (VRF) system into the Noosphere platform. It establishes a shared, epoch-based mechanism for generating and verifying random numbers, ensuring fairness and unpredictability for all connected dApps. The system leverages Merkle trees for pre-commitment and verification, combined with L2 block hashes for additional entropy, and includes built-in replay prevention. This enhancement provides a foundational service for dApps requiring secure and transparent randomness.

Highlights

• New VRF Module Introduction: This pull request introduces a new Verifiable Random Function (VRF) module within the src/v1_0_0/vrf/ directory, designed to provide epoch-based Merkle tree random values shared across all consumer dApps on a chain.
• INoosphereVRF Interface: A new public interface, INoosphereVRF.sol, has been added. It defines the contract for epoch management, request lifecycle (requesting and fulfilling random values), view functions for request status, configuration constants, and consumer management.
• NoosphereVRF Singleton Implementation: The core logic is implemented in NoosphereVRF.sol, a singleton contract. It handles epoch registration, global request ID assignment, Merkle proof verification, and replay prevention. It also incorporates a highly optimized assembly function for decoding base64 data URI outputs from the VRNG container.
• NoosphereVRFConsumer Abstract Contract: An abstract contract, NoosphereVRFConsumer.sol, is provided for dApps to inherit. This contract simplifies integration with the Noosphere compute pipeline and the NoosphereVRF singleton, exposing virtual hooks for handling received or expired random values and managing subscriptions.

Changelog

• src/v1_0_0/vrf/INoosphereVRF.sol
  • Added new interface for the Noosphere VRF singleton.
  • Defined events for epoch registration, low epoch slots, random value verification, expiration, and consumer management.
  • Included functions for epoch management (registerEpoch, getEpochRoot, getEpochRemaining, getCurrentEpoch).
  • Specified request lifecycle functions (requestRandomValue, fulfillRandomValue) for assigning and verifying random values.
  • Added view functions for nextRequestId, isRequestExpired, and getRequestBlock.
  • Defined configuration constants EPOCH_SIZE and BLOCKHASH_TIMEOUT.
  • Included functions for adding, removing, and checking authorized consumers.
• src/v1_0_0/vrf/NoosphereVRF.sol
  • Added new contract implementing the INoosphereVRF interface.
  • Integrated MerkleProof from OpenZeppelin and ArbSys for L2 block data.
  • Implemented storage for owner, next request ID, epoch roots, request block numbers, and authorized consumers.
  • Defined custom errors for access control and VRF-specific conditions.
  • Implemented onlyOwner and onlyConsumer modifiers.
  • Provided constructor to set the contract owner.
  • Implemented registerEpoch for owner-only epoch root registration.
  • Implemented requestRandomValue to assign global request IDs, record block numbers, and warn when epochs are running low.
  • Implemented fulfillRandomValue to resolve request IDs, decode output, verify Merkle proofs, and retrieve L2 block hashes for 2-party entropy.
  • Added consumer management functions (addConsumer, removeConsumer, isAuthorizedConsumer).
  • Implemented view functions for nextRequestId, isRequestExpired, getRequestBlock, getEpochRoot, getEpochRemaining, and getCurrentEpoch.
  • Included transferOwnership and typeAndVersion functions.
  • Developed an optimized _decodeRevealOutput assembly function for double base64 decoding of data URIs.
• src/v1_0_0/vrf/NoosphereVRFConsumer.sol
  • Added new abstract contract for dApps consuming Noosphere VRF.
  • Inherits from TransientComputeClient and Delegator.
  • Stored an immutable reference to the INoosphereVRF singleton.
  • Managed subscription ownership and user subscriptions.
  • Defined NotOwner and NotSubscriptionOwner errors.
  • Provided functions for createSubscription and cancelSubscription.
  • Implemented _requestRandomValue to interact with the VRF singleton and the compute pipeline.
  • Overrode _receiveCompute to delegate VRF verification to the NoosphereVRF singleton and call appropriate virtual hooks.
  • Defined virtual hooks _onRandomValueReceived and _onRandomValueExpired for dApp-specific logic.
  • Included view functions for getUserSubscriptions, getSubscriptionOwner, updateSigner, and getRouterAddress.
  • Added a _uint2str helper function for converting uint256 to string.

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[gemini-code-assist]

Code Review

This pull request introduces a well-structured and documented NoosphereVRF module, providing verifiable randomness through an epoch-based Merkle tree system. The use of a singleton for NoosphereVRF and an abstract NoosphereVRFConsumer is a solid design choice. My review focuses on improving correctness, scalability, and gas efficiency. I've identified a high-severity issue in cancelSubscription that leads to inconsistent state, a medium-severity scalability concern in getUserSubscriptions, and opportunities for gas optimization and clearer error handling within the complex data decoding logic in NoosphereVRF.