feat: Implement On-chain Verification Submission Engine

[akinboyewaSamson]

closes #284

Title

feat: Implement On-chain Verification Submission Engine

Overview

This PR introduces the Verification Submission Engine for TruthBounty V2, migrating the core verification handling fully on-chain as per the protocol specification. This ensures every verification becomes an immutable, independently auditable protocol record.

Key Features & Changes

• IVerificationSubmission Interface: Defines the canonical Verification data model, VerificationVerdict enum, and protocol events (VerificationSubmitted).
• VerificationSubmission Engine:
  • Validates claim eligibility via integration with IClaimRegistry (ensuring claim exists, is UnderVerification, and within the deadline).
  • Securely locks verifier stakes using native ERC-20 safeTransferFrom semantics (satisfying the "no immediate transfers to winners/losers" requirement).
  • Implements strict anti-duplication measures (mapping(uint256 => mapping(address => bool))) to prevent duplicate verifications from the same wallet.
  • Exposes optimized getter functions (getClaimVerifications, getVerifierStake) for downstream Aggregation and Settlement modules.
• Unit Tests & Gas Benchmarks: Added comprehensive Hardhat TypeScript tests (VerificationSubmission.test.ts) validating success conditions, failures, reentrancy guards, and gas profiles (approx. 272k gas for first submission, 238k for subsequent).

Related Issues

• Resolves: SC-004 (Verification Submission Engine)
• Depends On: SC-001 (On-Chain Claim Registry)