Add Event Processing Checkpoints

[Abd-Standard]

Description:
Persist the latest successfully processed ledger position so the listener can resume from a known checkpoint after interruption.

Scope:

Store processing checkpoints.
Update checkpoints after successful processing.
Resume from the last valid checkpoint.

Acceptance Criteria:

Restarting the listener does not require processing the entire history.
Checkpoints are only advanced after successful processing.
Recovery behavior is covered by tests.

[temisan0x]

@temisan0x has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Good day team, please i’d like to take on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @temisan0x to this issue.

[Jessepriase]

@Jessepriase has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

i would like to work on this issue

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

[Irhocko]

@Irhocko has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi Maintainer, i will like to work on this issue, please assign it to me.

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

[drips-wave]

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

🧑‍💻 @Jessepriase: 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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[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @Jessepriase as part of the Stellar Wave Program's 9th Wave 🥳

Moderator's reason: [Auto-assessed] The PR has an open status with no maintainer response across any of the four channels, and a thorough code contribution (PR #820) that implements checkpoint persistence, restoration, and comprehensive unit tests addressing all requirements of issue #783.

😎 @Jessepriase: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here.

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ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.