ops: Add a deprecation flag for legacy V1 pools

[AlAfiz]

Description

When we eventually launch V2 of the TradeFlow smart contracts, we cannot force users to migrate, but we need to signal that V1 is deprecated.
We need an Admin-only set_deprecated() flag on the pool contracts.
When deprecated is true, swaps should be permanently disabled, but liquidity withdrawals must remain permanently active.
This ensures a safe, non-custodial sunsetting process for older liquidity pairs.

Requirements

• Add a is_deprecated: bool flag to the pool's instance storage.
• Create an Admin-only function to toggle this flag to true (it should be an irreversible one-way toggle).
• Add a require(!is_deprecated) assertion to the swap and provide_liquidity functions.
• Ensure the remove_liquidity function intentionally bypasses this check so users can always exit.

[Mormentz]

@Mormentz has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi there, I can implement a safe deprecation mechanism for your V1 pools. I’ll add an irreversible is_deprecated flag, enforce it on swaps and liquidity provision, and ensure withdrawals remain fully functional, allowing a non-custodial sunsetting process.
Secure, user-friendly, and audit-ready. Ready to get started.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Mormentz to this issue.