Implement prioritized transaction queues and scheduled batch submission

[Just-Bamford]

Description

Problem

Transaction submission currently provides no high-level scheduling or prioritization model. Applications processing large workloads must manage ordering, retries, and batching themselves.

Solution

Introduce a transaction queue supporting low, normal, high, and critical priorities. The queue should schedule eligible transactions, group compatible submissions, and preserve ordering where transactions depend on one another.

Acceptance Criteria

• Transactions can be queued with a configurable priority
• Critical and high-priority transactions are processed ahead of lower priorities
• Batch size and scheduling intervals are configurable
• Dependent transactions cannot execute before their prerequisites
• Failed submissions return to the queue according to retry policy
• Duplicate transaction entries are prevented
• Queue state exposes pending, processing, completed, and failed items
• Tests cover priority ordering, batching, retries, dependencies, and cancellation
• Existing direct submission APIs remain unaffected

Note for Contributors

Avoid coupling queue state to a specific application runtime. Keep scheduling deterministic for tests and ensure a failed batch does not silently discard unrelated transactions.

[cythecode]

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

Reviewed the issue in detail and have a strong full-stack background that aligns well with this task. No blockers on my end—I’m ready to jump in and submit a PR shortly. Please assign it to me.

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

[Machundii]

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

Hi. I would like to work on this issue

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

[drips-wave]

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

🧑‍💻 @Machundii: 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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