Add idempotency-key middleware for mutation endpoints

[Chucks1093]

Summary
Add idempotency-key middleware for mutation endpoints

Scope

• add optional idempotency-key support for write routes\n- cache and replay successful duplicate requests safely\n- document expected header behavior

Acceptance Criteria

• scoped change is implemented with no unrelated file churn
• docs/tests are updated where applicable
• contributor can validate the outcome locally

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg

[FrostGraphix]

@FrostGraphix has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Can i take on this issue?

ETA: 6 hours.

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

[AbuJulaybeeb]

@AbuJulaybeeb has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi maintainer,
I would like to take on this

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[vhikdrums]

@vhikdrums has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I will like to work on this

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[wheval]

@wheval has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello i would love to work on this

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

[drips-wave]

Congratulations, @vhikdrums! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @vhikdrums: 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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