add tests for workspace booking contract functionality

[JoeX17]

closes #609

Description:
This PR introduces test coverage for the core book_workspace functionality within the workspace_booking smart contract. It ensures that successful bookings calculate costs correctly and execute the required token transfers, while also verifying that the contract strictly rejects overlapping booking attempts.

Key Changes:

• Added test_book_workspace_success:

• Utilizes setup_token to mint 10,000 tokens to the member address.

• Registers a Meeting Room workspace ("ws-001", capacity 10, rate 1,000/hr).

• Creates a 2-hour booking (booking-001) and asserts that the stored booking fields match the expected data (workspace_id, member, status: Active).

• Validates the contract's cost calculation logic (using ceiling division), ensuring amount_paid equals 2,000.

• Instantiates the TokenClient to verify the member's token balance correctly decreased from 10,000 to 8,000 after the transaction.

• Added test_book_workspace_conflict_fails:

• Registers a Hot Desk workspace (capacity 1).

• Creates an initial 1-hour booking.

• Attempts to create a second booking that overlaps with the first timeframe.

• Ensures the contract successfully rejects the overlapping booking by panicking with the expected BookingConflict = 7 error (Error(Contract, #7)).

Files Modified:

• contracts/workspace_booking/src/test.rs

Acceptance Criteria Met:

• All 7 tests (5 previous + 2 new) pass successfully using cargo test -p workspace_booking.
• test_book_workspace_success verifies the token balance decreased by exactly the amount_paid.
• test_book_workspace_success verifies the cost calculation logic (amount_paid == 2_000 for a 2-hour booking at 1_000/hr).
• test_book_workspace_conflict_fails correctly catches the Error(Contract, #7) panic.

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