logsql: fix stats_query_range metric order

[func25]

Fixes #1011

Checklist

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• My change adheres to VictoriaMetrics contributing guidelines.
• My change adheres to VictoriaMetrics development goals.

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Summary by cubic

Preserves metric order in /select/logsql/stats_query_range so it matches /select/logsql/stats_query. Fixes inconsistent series ordering observed in #1011.

• Bug Fixes
  • Parser now returns ordered metric fields via GetStatsLabelsAndMetricFieldsAddGroupingByTime.
  • Range handler uses this order to sort results; histogram buckets follow their parent metric’s order.
  • Added tests for parser order and an end-to-end range vs instant order check.
  • Updated changelog entry for the endpoint behavior.

^{Written for commit d6e0078. Summary will update on new commits.}

[cubic-dev-ai]

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