[Contract] Introduce property-based and invariant testing across all high-value contracts

[Solomonsolomonsolomon]

Move from example-driven tests toward deeper invariant and fuzz-style testing for accounting, authorization, timing, liquidation, and state-transition logic across the Soroban workspace.

[BigElv]

@BigElv has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would love to work on this issue

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

[dee-john]

@dee-john has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, I'd like to work on this issue! because I am very conversant with solving problems like this!

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

[Daveside9]

@Daveside9 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

can i do this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Daveside9 to this issue.

[amanosiadnan-cmyk]

@amanosiadnan-cmyk has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hii, i'd like to work on this issue

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