[Feature] Limit Order Execution via Off-Chain Keepers

[AlAfiz]

Description: Currently, TradeFlow only supports market orders. We want to allow users to place limit orders. The core contract must store the order intent, allowing off-chain "keepers" to execute the trade when the market price meets the order criteria.
Context / Motivation: Advanced traders require limit orders. Moving this on-chain allows TradeFlow to capture a more sophisticated demographic of DeFi users while rewarding keepers for network maintenance.
Acceptance Criteria: - [ ] Implement a create_limit_order function locking the user's input asset.

• Implement an execute_limit_order function callable by anyone, which verifies the current pool price satisfies the order.
• Route a small percentage of the input token as a bounty to the caller (keeper) of the execute function.
• Allow users to cancel unexecuted limit orders.
  Technical Pointers: Store limit orders in persistent storage mapped by an incremental ID or user Address. Emit a Soroban event (Env::events().publish()) upon order creation so off-chain backend indexing (TradeFlow-API) can track them easily.

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!