feat: Add token locking mechanism and SDK retry logic (#191, #170)

[midexol]

Description

This PR introduces two critical features across the smart contracts and the SDK:

1. Property Token Vesting (Property Token: Add token locking mechanism #191): Added a time-based token locking mechanism for vesting schedules inside the PropertyToken smart contract. Admin accounts can now assign unlock timestamps for fractional shares to prevent unauthorized transfers.
2. SDK Retry Logic (SDK: Add retry logic with exponential backoff #170): Implemented an intelligent exponential backoff retry mechanism inside PropChainClient wrapper to handle transient RPC failures.

Changes Made

• Smart Contracts: Updated PropertyToken struct, added VestingScheduleSet event, and TokenLocked error code. Modified transfer_from and safe_batch_transfer_from to enforce vesting timestamps.
• SDK: Added withExponentialBackoff in utils/connection.ts and wrapped network reads/writes in PropertyTokenClient.ts.

Closes #191
Closes #170

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[LaGodxy]

@midexol resolve conflicts.

[midexol]

@LaGodxy conflict resolved, review.