Add SeriesLabelsDeduplicated metrics

[lamida]

Follow up #14148. Add metrics on SeriesLabelsDeduplicator so that we can measure the impact better.

More context in MQE sync 17 Feb 2026 note.

What this PR does

Which issue(s) this PR fixes or relates to

Fixes #

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]. If changelog entry is not needed, please add the changelog-not-needed label to the PR.
• about-versioning.md updated with experimental features.

---

Note

Low Risk
Instrumentation-only change that adds counters and updates call sites to pass a registerer; main risk is minor metric/registry wiring issues in tests or embedded-querier deployments.

Overview
Adds Prometheus counters to SeriesLabelsDeduplicator to track how many series labels are processed vs deduplicated (cortex_querier_labels_deduplicator_processed_total, ..._deduplicated_total).

Threads a shared metrics instance through ContextWithNewSeriesLabelsDeduplicator and NewMemoryTrackingQueryable, updates affected tests/benchmarks to provide a registry, and adjusts integration metric-prefix assertions to ignore these new cortex_querier_* metrics when also exposed by embedded-querier Ruler.

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Bugbot Autofix prepared fixes for 1 of the 1 bugs found in the latest run.

• ✅ Fixed: Ignored prefixes ordered after broad matcher
  • Moved the ignore prefixes !cortex_querier_series_labels_total and !cortex_querier_series_labels_deduplicated_total before the broad cortex_querier matcher so they are evaluated first.

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Preview (10e282d7fe)

diff --git a/integration/asserts.go b/integration/asserts.go
--- a/integration/asserts.go
+++ b/integration/asserts.go
@@ -35,7 +35,7 @@
 	serviceMetricsPrefixes = map[ServiceType][]string{
 		Distributor:    {},
 		Ingester:       {"!cortex_ingester_client", "cortex_ingester"},                                                                                                                                                                              // The metrics prefix cortex_ingester_client may be used by other components so we ignore it.
-		Querier:        {"!cortex_querier_storegateway", "!cortex_querier_blocks", "!cortex_querier_queries", "!cortex_querier_query", "cortex_querier", "!cortex_querier_series_labels_total", "!cortex_querier_series_labels_deduplicated_total"}, // The metrics prefix cortex_querier_storegateway, cortex_querier_blocks, cortex_querier_queries, cortex_querier_query, cortex_querier_series_labels_total, and cortex_querier_series_labels_deduplicated_total may be used by other components so we ignore it.
+		Querier:        {"!cortex_querier_storegateway", "!cortex_querier_blocks", "!cortex_querier_queries", "!cortex_querier_query", "!cortex_querier_series_labels_total", "!cortex_querier_series_labels_deduplicated_total", "cortex_querier"}, // The metrics prefix cortex_querier_storegateway, cortex_querier_blocks, cortex_querier_queries, cortex_querier_query, cortex_querier_series_labels_total, and cortex_querier_series_labels_deduplicated_total may be used by other components so we ignore it.
 		QueryFrontend:  {"cortex_frontend", "cortex_query_frontend"},
 		QueryScheduler: {"cortex_query_scheduler"},
 		AlertManager:   {"cortex_alertmanager"},

[charleskorn]

What other component would see the new metrics? The ruler?

[lamida]

Yes we added !cortex_querier_series_labels_total", "!cortex_querier_series_labels_deduplicated_total" on that line 38 because Ruler component also can use it when using embedded mode querier.

[charleskorn]

Could you please add a comment here explaining that?

[lamida]

Updated in the last two commits