resource_manager: add replayable per-second RU observations

[JmPotato]

Issue Number: ref #1545

Clients report accumulated RU consumption asynchronously, so PD cannot reconstruct aligned one-second peaks from report-arrival times.

Add the optional Consumption.ru_by_second observation ledger. Each payload identifies a contiguous range of closed UTC seconds and carries immutable, signed RRU/WRU contributions, including zero seconds. The outer client ID, resource group, keyspace and source kind identify the producer; overlapping ranges can be replayed and deduplicated by the consumer. An absent ledger means unsupported observation, not zero consumption.

The existing scalar consumption fields retain their billing and token-allocation semantics. Regenerate the Go bindings and protocol compatibility lock.

Validation: make check and go test ./pkg/resource_manager. Local PD/TiDB SQL integration verified transport and reconstruction against raw confirmed-accounting logs; the PD follow-up contains the aggregation and end-to-end evidence.

Summary by CodeRabbit

• New Features
  • Added per-second resource consumption observations, including UTC start times and repeated consumption buckets.
  • Consumption buckets now report signed read and write resource usage values.
  • These observations are informational and do not affect token allocation or billing.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📥 Commits

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• proto/resource_manager.proto

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📝 Walkthrough

Walkthrough

The protobuf schema adds an optional per-second RU observation ledger to Consumption. It defines timestamped buckets with signed read and write settlement values. The ledger is separate from token allocation and billing.

Changes

RU consumption ledger

Layer / File(s)	Summary
Ledger message contract proto/resource_manager.proto	Consumption adds optional field ru_by_second. New RUConsumptionBySecond and RUConsumptionBucket messages define the timestamp, bucket list, and signed rru and wru values.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Suggested reviewers: disksing

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding replayable per-second RU observations.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

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_{A rabbit hops through protobuf snow
New RU buckets line up in a row
Reads and writes keep signed score
The ledger observes, but bills no more
Timestamps guide each careful flow}

_{Comment @coderabbitai help to get the list of available commands.}

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