test: Integration suite for bridge <-> oracle cross-contract resolution

[nanaf6203-bit]

Add a focused integration test under tests/integration_bridge_oracle.rs covering end-to-end oracle update -> bridge attestation -> cross-chain verification.

[Killerjunior]

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[Dataguru-tech]

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

Hi maintainer, I would like to work on this issue

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