feat: cancel public sale

[julienbrs]

Description

During the funding phase, admin can call cancel_mint for an emergency case. The mint is then cancelled and each user can call redeem_investment to get their money back by burning their unused SFT for USDC invested

Acceptance Criteria

• [x] Only the admin can call cancel_mint. Unauthorized users must be rejected.
• [x] The minting process must stop at the same time cancel_mint is called.
• [x] Users can call redeem_investment to reclaim their USDC after mint cancellation.
• [x] SFTs must be burned before USDC is transferred during redeem_investment.
• [x] Emit correct events

Additional context

One issue might be if users invest with multiple currencies (i.e STARK, USDC, ETH). Option 1: We keep track of how people invested (which currency for which amount) in a mapping. Option 2: We refund everyone in stablecoin (USDC) thanks to the minting price which is constant. However, Carbonable should beforehand swap all the ETH, STARK, etc..

Volatility might be an issue: Bob invest 1ETH worth $2k, mint is cancelled but ETH dumped by 50%. Now Bob got $1k back, like if he was holding ETH (but if he used his ETH to pay that means he probably didn't want to hold it).

[tekkac]

+1 We had something like this in mind, your version being more simple and elegant to me. I don't think swapping is needed since public_buy is only possible in USDC. Using other tokens is possible yet only as a Carbonable service.