test: add test verifying proposal cancel refunds tokens to proposer

[Adedayo-Data]

Description

This PR adds test coverage verifying that canceling a proposal successfully refunds the proposer's locked deposit.

Changes

• Added test_cancel_refunds_deposit_to_proposer in contracts/governance-dao/src/test.rs.
• The test verifies:
  1. Proposer's token balance decreases by proposal_threshold when the proposal is created.
  2. Proposer's token balance increases back to its original state when the proposal is canceled.
• Restored test_proposal_expires_after_voting_period compilation with the required arguments.

closes #209

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