feat: add emergency pause for all pools

[dinahmaccodes]

Closes #19

Add Global Admin Pause/Unpause Functionality

Summary

I introduced a global emergency pause mechanism allowing the admin to halt all mutative contract operations in case of critical bugs or exploits.

Changes

• Admin Authorization: Admin address set during contract initialization
• Pause State Management: Boolean flag stored in instance storage (IsPaused)
• Mutative Function Guards: Added pause checks to:
  • create_campaign
  • save_pool
  • update_pool_state
• Admin Controls:
  • pause() - Halts all mutative operations (admin only)
  • unpause() - Resumes normal operations (admin only)
• Events: Emits contract_paused and contract_unpaused events
• Error Handling: Added NotInitialized error for unset admin scenarios

Safety Features

• Only the contract admin can pause/unpause
• Prevents double-pause and double-unpause operations
• Read operations remain available during pause
• No impact on existing pool-specific pause functionality

Testing

• All 30 existing tests pass
• Added test coverage for pause blocking update_pool_state
• Verified admin-only authorization enforcement

Notes

This is a contract-wide safety mechanism. Per-pool pause functionality is tracked separately in another issue as stated in issue I was assigned.

[dinahmaccodes]

Fixed conflicts @martinvibes

All tests passing once more

[martinvibes]

@dinahmaccodes pls fix conflict and make sure CI is passing