feat(backend): Implement batch contract method simulation

[Viky207]

Problem

Single-operation simulation only.

Task

Add batch simulation endpoint.

Acceptance Criteria

• POST /transactions/batch-simulate accepts array
• Independent per-operation results
• Atomic flag for batch failure
• Rate limited 10/min
• Max 10 ops per batch

[milkthestallie]

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

Hello, I’d be glad to contribute to this issue and would appreciate the opportunity to work on it. Thanks for considering.

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

[kceeglo345-dev]

@kceeglo345-dev has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I would love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @kceeglo345-dev to this issue.

[drips-wave]

Congratulations, @kceeglo345-dev! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @kceeglo345-dev: 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.

Warning

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