Assert emitted events in all unit tests

[phertyameen]

Issue #60: Assert emitted events in all unit tests

Category: Testing
Repo: bridgelet-core (Soroban / Rust)

Description

Every unit test that triggers a state change should assert the corresponding event was emitted with correct fields. Use Soroban's env.events().all() in the test harness.

Acceptance Criteria

• Rust implementation complete
• cargo test passing
• Integration test on local Stellar sandbox passing
• Docs updated (docs/ or inline rustdoc)
• Reviewed and merged