[Contract] Implement Token-Weighted Voting Module for Asset Proposals

[yusuftomilola]

Governance mechanism allowing token holders to vote on proposals (e.g. detokenization, asset sale) with votes weighted by token balance.

Requirements

cast_vote(env, asset_id, proposal_id, voter):

• Voter must authenticate
• Voter must hold tokens and not have already voted
• Adds the voter's token balance to the proposal's running tally
• Marks voter as having voted (prevents double voting)
• Emits a vote_cast event

get_vote_tally(env, asset_id, proposal_id) — Returns cumulative votes cast

has_voted(env, asset_id, proposal_id, voter) — Read-only

proposal_passed(env, asset_id, proposal_id):

• Passes if tally ≥ min_voting_threshold (set during tokenization)

Acceptance Criteria

• Double voting returns Error::AlreadyVoted
• Vote weight equals voter's token balance at time of voting
• proposal_passed respects the min_voting_threshold