Issue 123

[samieazubike]

Description

Implements approve_withdraw and reject_withdraw on GroupTreasuryContract, adding the multisig voting layer (issue #123).

Contract changes

• storage.rs:
  • New DataKey::Vote(u32, Address) — per-voter record keyed by (proposal_id, voter), the mechanism that blocks double-voting (the WithdrawProposal struct only carried approvals/rejections counters).
  • New events: WithdrawVoteCastEvent, ProposalApprovedEvent, ProposalRejectedEvent.
• lib.rs:
  • approve_withdraw(env, approver, proposal_id) — records the vote, increments approvals, and transitions the proposal to Passed (approved) + emits ProposalApprovedEvent once approvals >= threshold.
  • reject_withdraw(env, rejecter, proposal_id) — increments rejections, and transitions to Rejected + emits ProposalRejectedEvent once the blocking minority (members - threshold + 1) is reached.
  • get_proposal(env, proposal_id) — read-only view of a proposal.
  • require_votable(...) — shared guard: require_auth → member check → load proposal → ensure Active, not expired, not already voted.

Notes

• Status naming reuses the already-merged enum: Pending = Active, Approved = Passed (no enum churn, so Implement execute_withdraw #124 execute_withdraw can build on Passed → Executed).
• propose_withdraw (Implement propose_withdraw on Group Treasury contract #122) is not implemented yet, so tests seed proposals directly into storage via an env.as_contract helper.

Security

• require_auth on every vote; member-only voting; one vote per address per proposal (dedicated storage key, not a counter re-tally); no voting on non-pending or expired proposals; counters bounded by member count under overflow-checks = true. No token movement occurs here, so there is no reentrancy surface.

Tests — 11 new tests covering every acceptance criterion plus edges (threshold transition, below-threshold, double-vote panic, vote-switch panic, non-member panic, non-pending panic, expired panic, blocking-minority rejection, unknown-proposal panic, missing-auth panic).

• cargo test -p group_treasury → 31 passed, 0 failed
• cargo clippy clean on new code; cargo build --release (no_std wasm) compiles.

Closes #123

Type of change

• Bug fix
• New feature
• Documentation update
• Other

Checklist

• I have read the contributing guidelines
• I have tested my changes locally
• My code follows the project's coding standards

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