feat(all): add contract upgradability, batch payouts, and proposal cancellation

[SaintSammi]

feat(all): add contract upgradability, batch payouts, and proposal cancellation

Summary

This PR resolves three open issues by adding new functionality across the core contracts.

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#61 — Smart Contract Upgradability

Added upgrade_contract(env, admin, new_wasm_hash) to all six core contracts:

• BadgeNFT, CourseRegistry, QuestEngine, RewardPool, StakeVault, Governance

• Requires admin.require_auth() and verifies the caller is the stored admin

• Calls env.deployer().update_current_contract_wasm(new_wasm_hash)

• Emits a ContractUpgraded event

• All persistent storage state is preserved across upgrades

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#62 — Batch Payouts for Quests

Added batch_review_submissions(env, employer, quest_id, learners) to QuestEngine:

• Requires employer.require_auth() once for the whole batch
• Iterates over all learner addresses and executes the full review_submission logic per learner (15% platform fee + staking multiplier)
• Emits individual SubmissionReviewed events and a final BatchReviewed event

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#60 — Cancel Proposal (Governance)

Added cancel_proposal(env, caller, proposal_id) to Governance:

• Requires caller.require_auth()
• Verifies caller is the original proposer or the protocol admin
• Asserts the voting period is still active and the proposal has not already been executed
• Sets executed = true to lock the proposal from further votes or execution
• Emits a ProposalCancelled event

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Testing

• Tests added for all three features in their respective test.rs files
• All existing tests continue to pass

Closes #60
Closes #61
Closes #62

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