feat(creator-keys): add dividend reinvestment function (#805)

[Oluwasuyi-Oluwatimilehin-Daniel]

Summary

• Implemented the reinvest_dividend entry point on CreatorKeysContract allowing key holders to atomically convert their unclaimed dividend balance into additional creator keys via the bonding curve in a single transaction.
• Computed claimable dividends and iteratively executed whole key purchases at incremental bonding curve prices while remaining >= key_price and supply/wallet caps permit.
• Automatically refunded/credited any residual dividend balance below the incremental price of 1 key to the caller's balance.
• Reset the pending unclaimed dividend balance and updated the accumulator checkpoint to the current global value.
• Reverted with ContractError::NoDividendToClaim when called with zero unclaimed dividend balance.
• Accrued trading fees, protocol trade fees, royalties, incremented creator supply and holder balance, and updated last_buy_timestamp for anti-flash-trade sell lockups.
• Emitted a structured DividendReinvestedEvent (div_reinv) containing wallet, key_id, keys_bought, remainder_returned, and ledger.
• Added comprehensive integration test coverage in creator-keys/tests/dividend_reinvestment.rs covering happy path compounding, remainder returns, zero dividend errors, security guards, and event verification.

Closes #805

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

Checklist

• Linked issue or backlog item
• Added or updated creator-keys unit/integration tests for every changed contract behavior, including failure paths for new or reachable ContractError variants
• Ran cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings, and cargo test --workspace, or explained exactly why a command was not run
• Reviewed persistent storage changes against docs/storage-key-invariants.md; any storage layout change includes a migration/backward-compatibility note
• Confirmed event names, topic order, payload field order, and field meanings remain compatible with docs/contract-event-conventions.md, or documented the breaking change and versioning plan
• Updated docs for any changed public contract interface, read-only method, event schema, storage behavior, fee logic, or deployment workflow
• Scope stays limited to one contract concern and does not include unrelated formatting, lockfile, generated artifact, or dependency changes

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[Chucks1093]

✅ CI Passed — ⚠️ Merge Conflict

CI is green but this PR has a merge conflict with main and cannot be auto-merged.

To fix:

1. Pull the latest main: git fetch origin && git checkout your-branch && git merge origin/main
2. Resolve any conflicts in the affected files
3. Run cargo build and cargo fmt to verify everything still compiles and is formatted
4. Push the resolved branch — CI will re-run and the PR will be auto-merged once it passes

[Chucks1093]

Fix MC

[Chucks1093]

Merge Conflict