Add SDK graceful shutdown

[Kingsman-99]

Label: complexity: high
Points: 200

Description

Abruptly terminating a process with an active SDK instance can lose queued operations and corrupt cache state. This issue adds shutdown() that flushes pending operations, persists cache to disk, closes all connections, and resolves when cleanup is complete.

Technical Context

Involves src/client.ts. shutdown(): Promise<void> drains the operation queue, calls cache.persist() if persistence is configured, removes all event listeners, and nullifies internal references. Register process.on('SIGTERM', () => client.shutdown()) automatically when in Node.js environment.

Acceptance Criteria

• shutdown(): Promise<void> exported on StellarSplitClient
• Pending queued operations flushed before shutdown completes
• Cache persisted to disk when persistence configured
• All event listeners removed on shutdown
• Test verifies queued operation completes before shutdown resolves
• All existing tests pass
• TypeScript strict mode — zero any types

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[ShantelPeters]

@ShantelPeters has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, i would like to work on this issue , kindly assign i am ready to work

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

[oraimoitel]

@oraimoitel has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Good day maintainer, I will be glad if I will be given an opportunity to contribute on this repo. I am an experienced full stack developer with 3 yrs of experience

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

[Onomebello]

@Onomebello has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello i would like to work on this issue

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[drips-wave]

Congratulations, @Onomebello! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Onomebello: 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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