SDK: timeout and retry options

[blockchain-maxis]

fetch calls hang indefinitely on a stalled network.

Acceptance: configurable timeout via AbortController plus bounded retries on 5xx;
defaults documented; tests with a mocked fetch.

[samuelelijah585]

@samuelelijah585 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, I've reviewed the issue and its acceptance criteria, and I'm confident I can deliver a solution that meets the requirements. I'd appreciate it if you could assign this issue to me. Thank you!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @samuelelijah585 to this issue.

[drips-wave]

Congratulations, @samuelelijah585! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @samuelelijah585: 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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