feat: add slowest query interval metric

[pratik50]

Summary

• Track the slowest completed non-streaming query in each analytics interval.
• Export the duration through parseable_slowest_query_duration_seconds.
• Add time_range_seconds and query_type labels.
• Reset the metric after each interval to avoid sending stale data.
• Streaming queries are not included.

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Walkthrough

SQL count and non-streaming query handlers now record execution and requested range durations. The metrics module retains the longest recorded query in an interval and publishes its duration, range, and query type through a registered gauge.

Changes

Slowest Query Metrics

Layer / File(s)	Summary
Track and publish the slowest query src/metrics/mod.rs	The metrics module adds SQL and PromQL query types, stores the strictly longest query snapshot, and refreshes a gauge with its duration, range, and type. Tests cover snapshot selection and gauge refresh.
Record SQL handler query durations src/handlers/http/query.rs	The handler calculates the requested time-range duration and passes it to count and non-streaming handlers. Those handlers record query metrics alongside the existing execution-time metric. Streaming dispatch is unchanged.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Suggested reviewers: nikhilsinhaparseable

Merge Risk: 🟡 Moderate · up to b72fc

The new slowest-query metric will not report production queries. Connect its refresh to the production interval before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 36.36% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding a metric for the slowest query in each interval.
Description check	✅ Passed	The description clearly states the goal, metric name, labels, reset behavior, and exclusion of streaming queries. It does not include the template's explicit rationale or testing, comments, and docume…

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✨ Finishing Touches

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---

_{A rabbit watched the query run,
And timed its path beneath the sun.
The longest wait was marked with care,
Its range and kind now travel there.
The gauge wakes fresh for each new span.}

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

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Actionable comments posted: 1

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Inline comments:
In `@src/metrics/mod.rs`:
- Around line 111-123: Update the existing PROCESS_METRICS_SAMPLE_INTERVAL path
to call refresh_query_metrics every five seconds, so production publishes
accumulated slowest-query samples and resets the accumulator; leave the
refresh_query_metrics implementation unchanged.

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📥 Commits

Reviewing files that changed from the base of the PR and between b09ab6f and b72fc9c.

📒 Files selected for processing (2)

• src/handlers/http/query.rs
• src/metrics/mod.rs

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