No minimum balance enforcement after withdrawal in lending pool

[Junman140]

acbu_lending_pool/src/lib.rs: After a withdraw, the lender's remaining balance may be 1 stroop. Future operations on dust balances cause precision errors and unnecessary storage entries.

[Elizabethxxx]

@Elizabethxxx has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hy maintainer, I can resolve this issue within 24hours. I am an oss contributor with enough experience

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

[drips-wave]

Congratulations, @Elizabethxxx! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Elizabethxxx: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🦊 GrantFox — @Elizabethxxx has been assigned to this issue!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #311)
2. Your PR will be reviewed by the Pi-Defi-world maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@Elizabethxxx's PR #406 was approved and merged by @Junman140.

🏆 @Elizabethxxx: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (226 total points). Track your full progress on GrantFox.

👏 Great work, @Elizabethxxx! Keep contributing to Pi-Defi-world.