Test `payment_received` event topics and data fields

[Kingsman-99]

Description

payment_received in contracts/split/src/events.rs publishes an event with topics (split, paid, invoice_id) and data (payer, amount, event_seq). There is no test asserting that the event is published with the correct field values after a call to this function.

Acceptance Criteria

• Add a test named payment_received_event_has_correct_fields in tests/event_log_tests.rs or a new file
• Call payment_received(&env, 42, &payer, 1000) and capture published events
• Assert topics include invoice_id == 42, data includes payer address and amount == 1000
• cargo test passes

Context

• Target file: contracts/split/src/events.rs (test in tests/event_log_tests.rs)
• Use soroban_sdk::testutils::Events

[famvilianity-eng]

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[grantfox-oss]

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@famvilianity-eng's PR #644 was approved and merged by @Kingsman-99.

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