Add `ledger_sequence` to `invoice_cloned` event data

[Kingsman-99]

Description

invoice_cloned in contracts/split/src/events.rs currently publishes an empty data payload (). Adding the ledger_sequence at which the clone occurred gives indexers a timestamp anchor without needing to query ledger metadata separately.

Acceptance Criteria

• Modify invoice_cloned to publish (env.ledger().sequence(),) as the event data instead of ()
• Update any tests that assert the exact data payload of the cloned event
• cargo test passes

Context

• Target file: contracts/split/src/events.rs

[Onomebello]

@Onomebello has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

please assign me this issues

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@Onomebello's PR #656 was approved and merged by @Kingsman-99.

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This issue has been completed by @Onomebello as part of the Stellar Wave Program's 8th Wave 🥳

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