perf(diagnostics): bound RPC latency aggregation

[beruro]

Problem

RPC latency aggregation and diagnostics retention can grow cardinality or preserve more raw detail than needed, increasing memory/persistence cost and privacy risk.

Solution

• Bound RPC duration aggregation cardinality while preserving stable buckets.
• Sanitize runtime counters before persistence/submission.
• Retain only diagnostics detail required for performance investigation.
• Add bucket-edge, queue, and sanitization coverage.
• Validation: focused Vitest, TypeScript typecheck/ESLint, Rust usage-diagnostics tests/check/rustfmt, and diff check.

Potential risks

• Over-aggressive sanitization or bucketing could remove useful diagnostic distinctions.
• Bucket boundaries must remain stable for comparisons across versions.
• This PR is independent of the async-resource and session stacks.