resource_manager: add signed RU settlement report

[YuhaoZhang00]

Summary

• Add TokenBucketRequest.settlement_since_last_request for signed RRU/WRU token settlement reporting.
• Clarify consumption_since_last_request as actual resource usage for stats and metering.

Related

• Supports client/resource_group: add RC paging pre-charge with PredictedReadBytes hint tikv/pd#10611.

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[YuhaoZhang00]

/hold