feat: Add fail-safe handling for expired requests, zero-value transfers, and zero-address init

[nottherealalanturing]

closes #129, closes #128, closes #127

This pull request introduces critical fail-safe handling and validations to the Oraculum smart contracts. These updates ensure robust execution by preventing invalid states and edge cases from being processed.

Key Changes Implemented:

• Expired Payment Requests (CT-50):
  Added strict timestamp validations to ensure that expired payment requests immediately revert with a deterministic error. This guarantees that outdated transactions are not processed after their validity window has elapsed.

• Zero-Value Transfer Requests (CT-49):
  Implemented a validation check to block token transfer requests where the amount is exactly zero. This prevents wasted compute cycles, mitigates potential spam vectors, and ensures all transfers hold actual value.

• Zero-Address Admin Initialization (CT-48):
  Added a sanity check during contract initialization to verify that the provided admin address is not the zero address or an invalid identifier. This protects the contract from becoming permanently locked or unmanageable upon deployment.

These changes enhance the overall security posture and reliability of the protocol's core operations.

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[Qoder-Voidd]

LGTM