(WIP): Fix memory leak when soft-deleting tenant registries

[santihernandezc]

Fixes #746

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Note

Archives and deduplicates counters/histograms/summaries from soft-deleted tenant registries and includes them in aggregations; adds tests and a benchmark.

• Metrics (TenantRegistries):
  • Add archived MetricFamilyMap to store metrics from soft-deleted registries (excludes gauges).
  • Replace soft-delete flow: AddTenantRegistry and RemoveTenantRegistry now call archiveTenantRegistry and remove the registry; keep old RemoveTenantRegistry_Old for reference.
  • Implement archival with label-based dedup and value aggregation via deduplicateMetrics, getMetricLabelSignature, and mergeMetricValues (counters/summaries/histograms only).
  • BuildMetricFamiliesPerTenant: include archived metrics as an empty-tenant entry; copy archived under lock to avoid concurrent access.
• Tests/Benchmarks:
  • Add TestSoftRemoveTenantRegistryDeduplication ensuring deduplication and accumulation; gauges not archived.
  • Add BenchmarkSoftRemoveMemoryLeak to verify bounded memory on tenant churn.

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[cursor]

Bug: Inconsistent metric type used for deduplication vs storage

The deduplicateMetrics function is called with m.GetType() (the new metric's type), but the resulting MetricFamily is created with v.Type (the existing metric's type). If types somehow differ, the merged metrics would be processed using one type but the family would be labeled with a different type, causing inconsistent metric data. The type used for merging and for the family should be consistent.