Add helper for asserting contract event fields in test assertions

[Chucks1093]

Summary

Tests that verify emitted contract events repeat the same boilerplate to extract and compare event fields from the transaction result meta. A shared test helper should reduce this to a single assertion call.

Scope

• Add assert_event(env, contract_id, topic, expected_fields) test helper
• Helper should extract events from the transaction result, filter by topic, and compare fields
• Add usage in at least two existing event-emitting test cases to validate the helper

Acceptance Criteria

• Helper filters events by topic and contract correctly
• Field comparison fails with a clear message on mismatch
• Used in at least two existing test cases
• No duplication of event extraction boilerplate in updated tests

ETA: 12 hours

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Coordinate on Telegram

[GBOYEE]

Hey team — I can handle this one. I'll write the missing test coverage and wire it in. I can put up a PR for this once claimed.

[mxrtins04]

Hi maintainer, can i be assigned this issue pleasee?