feat: Implement debt_token contracts with tests

[FabienCoutant]

Feature Request

Describe the Feature Request

Implement and tests the debt_token

Describe Preferred Solution

Main logic

File: src/core/debt_token.cairo

Tests

Implement the following tests files:

• tests/integration/core/debt_token/set_delay/test_burn.cairo
• tests/integration/core/debt_token/mint/test_mint.cairo
• tests/integration/core/debt_token/transfer/test_transfer.cairo
• tests/integration/core/debt_token/transfer_from/test_transfer_from.cairo
• tests/integration/core/debt_token/add_whitelist/test_add_whitelist.cairo
• tests/integration/core/debt_token/remove_whitelist/test_remove_whitelist.cairo
• tests/integration/core/debt_token/return_from_pool/test_return_from_pool.cairo
• tests/integration/core/debt_token/send_to_pool/test_send_to_pool.cairo
• tests/integration/core/debt_token/mint_from_whitelisted_contract/test_mint_from_whitelisted_contract.cairo
• tests/integration/core/debt_token/emergency_stop_minting/test_emergency_stop_minting.cairo
• tests/integration/core/debt_token/burn_from_whitelisted_contract/test_burn_from_whitelisted_contract.cairo

Requirement

Issue to complete before:
#1

Related Code

DebtToken