Add unit tests for the contract correctly rejecting a sell of zero keys

[Chucks1093]

Summary

A sell request with an amount of 0 should panic with zero_amount before any payout calculation occurs.

Scope

• Test selling 0 keys panics with zero_amount
• Assert supply unchanged after the panic
• Assert no KeySold event emitted

Acceptance Criteria

• Selling 0 keys panics with zero_amount
• Supply unchanged after panic
• No event emitted

ETA: 12 hours

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[badmusdare4]

@badmusdare4 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I can resolve this problem,please assign it to me maintainer.

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[mayborn005]

@mayborn005 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello @maintainer, Interested in working on this. I'll ensure the implementation is clean, tested, and aligned with project standards.

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[Appsoft1000]

@Appsoft1000 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

hi can i work on this

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[Unclebaffa]

@Unclebaffa has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi! I've carefully reviewed the entire task description and fully understand the requirements and expected outcome.
I have experience working on similar tasks and I'm confident I can complete this within about an hour. I'd be happy to take ownership of this issue and submit a clean, well-tested solution promptly.
If it's available, please assign it to me. Thank you!

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[David-282]

@David-282 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

KIndly assig this issue to me

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