[Wave 9] Add state migration tests across contract versions

[truthixify]

Problem

Upgrade authority tests prove who can upgrade, but they do not prove that existing storage and event state remains usable after a contract upgrade.

Done when

• Create representative pre-upgrade storage snapshots.
• Apply each supported upgrade in a test environment.
• Assert old records remain readable and new writes use the expected schema.
• Document rollback and incompatible migration behavior.

[Clinton6801]

@Clinton6801 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello boss, I've gone through the issue description and i would love to work on this issue , kindly assign me

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[samkiell]

@samkiell has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

hello, i would love to work on this, let me take this off your plate asap.

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[AladeDavidToluwanimi]

@AladeDavidToluwanimi has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello! I'd love to contribute here. I can commit the time to get this done properly and promptly.

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[TeeGeason05]

@TeeGeason05 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello Maintainer, I’d be happy to take this issue. I’m ready to start immediately and will aim to have a clean, thoroughly tested PR ready within 1–2 hours.

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[ojuotimi932]

@ojuotimi932 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi Maintainer, can i work on this. Kindly assign

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