Add structured log for each indexer batch start and completion with ledger range and event count

[Chucks1093]

Summary

Each time the indexer processes a batch of ledgers, there is no log marking the start or end of the batch. An info-level log at the start and a debug-level log at completion would give operators a clear picture of indexer throughput and batch size without requiring database queries.

Scope

• Emit an info-level log at batch start with fields: from_ledger, to_ledger, batch_size
• Emit a debug-level log at batch completion with fields: from_ledger, to_ledger, events_processed, duration_ms
• Both logs emitted per batch, not per individual ledger within the batch

Acceptance Criteria

• Info log emitted at batch start with correct ledger range and batch size
• Debug log emitted at batch completion with correct event count and duration
• Logs emitted once per batch, not once per ledger
• duration_ms reflects wall-clock time from batch start to completion

ETA: 12 hours

---

Coordinate on Telegram

[KingDavid9999]

@KingDavid9999 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi maintainer, I'd very much appreciate the opportunity to work on this issue.
Having reviewed the acceptance criteria, I'm confident that I'd be able to have a PR up shortly after being assigned.
Kindly assign this issue to me.
Thank you!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @KingDavid9999 to this issue.

[omoh5]

@omoh5 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

please assign this to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @omoh5 to this issue.

[ZeePearl56]

@ZeePearl56 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would like to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ZeePearl56 to this issue.

[drips-wave]

Congratulations, @KingDavid9999! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @KingDavid9999: 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

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@KingDavid9999's PR #658 was approved and merged by @Chucks1093.

🏆 @KingDavid9999: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (271 total points). Track your full progress on GrantFox.

👏 Great work, @KingDavid9999! Keep contributing to accesslayerorg.

[drips-wave]

This issue has been completed by @KingDavid9999 as part of the Stellar Wave Program's 7th Wave 🥳

😎 @KingDavid9999: 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. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.