Implement stream splitting into two sub-streams

[Chuks-coderr]

Overview

Add a split_stream instruction that cancels an active stream and creates two new streams dividing the remaining balance by a specified ratio.

Acceptance Criteria

• Ratio expressed as basis points (0–10000)
• Original stream cancelled atomically with sub-stream creation
• Accumulated claimable at split time distributed proportionally
• Both sub-streams inherit original end_time and cliff_end_time
• No tokens lost or duplicated (invariant enforced in tests)

[kodinaka30-ship-it]

@kodinaka30-ship-it has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Maintainer,
I would like to work on this issue because I have experience implementing atomic stream mutation logic in smart contracts. I can add split_stream with basis-point ratio validation, atomic cancellation and sub-stream creation, proportional distribution of accumulated claimable, correct inheritance of end_time and cliff_end_time, and tests enforcing the no-loss/no-duplication invariant.
Please kindly assign.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @kodinaka30-ship-it to this issue.

[QwinDivy]

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

Hi Maintainer, I'd love to take this one on. I've gone through the codebase and I'm comfortable with the approach needed here. I'll keep the change focused, add tests, and make sure CI stays green. Happy to open a draft early so we can align on direction.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @QwinDivy to this issue.

[drips-wave]

Congratulations, @QwinDivy! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @QwinDivy: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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