[Testing] Setup Property-Based Testing for Contract Invariants (#99)

[AdityaK9822]

Closes #99

This PR integrates the proptest framework to ensure our critical task invariants consistently hold under sequences of randomized actions.

Changes Included:

• Added proptest = "1.5.0" into [dev-dependencies] for contract.
• Created a robust property testing module (contract/src/proptest.rs) executing hundreds of random permutations for each configured property.
• Included validations for:
  • Task Registration/Creation: Random parameter coverage scaling limits ensuring no edge-case overflows trap new tasks.
  • State Transitions: Continuous sequences varying pause/resume logic ensuring bounds function properly when hit recursively.
  • Financial Balances: Mocked token behavior confirming randomized deposit/withdraw sequences track mathematically identically against internal state values rejecting all insufficient withdrawal bounds securely.

ETA Completed: Under 2 days (as required).

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[ayomideadeniran]

Pr under review.