Add vesting / scheduled token release for RWA investors

[Prasiejames]

Problem

The RWA token supports mint() and mint_to_investor() for immediate token issuance. Real-world asset deals often require vesting schedules (cliff + linear release) for regulatory compliance or investor lock-ups.

Expected Behavior

A VestingContract that holds tokens and releases them to beneficiaries according to a schedule.

Proposed Solution

Create a new contracts/vesting/ contract:

pub fn create_vesting(
    beneficiary: Address,
    total_amount: i128,
    cliff_duration_ledgers: u32,
    vest_duration_ledgers: u32,
    start_ledger: u32,
) -> u64 /* vesting_id */

pub fn claim_vested(vesting_id: u64) -> i128
pub fn get_vesting_schedule(vesting_id: u64) -> VestingSchedule
pub fn revoke(vesting_id: u64) /* admin only */

The calculation: vested = total * min(1, (current - start) / vest_duration), with nothing before cliff.

Dependencies

• New contract that holds RWA tokens and transfers on vesting