Optimize the metric SDK

[MrAlias]

Optimize the Metric SDK CPU and memory usage to improve performance.

• Investigate Counter collection performance #7592
• Concurrent performance of exemplar reservoir is limited by locking #7388
• Consider using xxHash instead of fnv64-1a #7371
• Improve performance of attribute.NewSet #7743
• Optimize fixedsize reservoir #7447
• Improve concurrent performance of exponential histogram measurements #7535
• refactor: expoBuckets uses a circular buffer to avoid shifts #7706
• Add benchmarks for end-to-end metrics SDK usage #7768
• PoC: Bound Instruments: Add WithAttributes to instruments. #7790
• Testing: Run sync measure benchmarks in parallel #7113
• Add benchmark for map access using attribute Equivalent #7123
• Use Set hash in Distinct (2nd attempt) #7175
• Optimize locking for metric aggregations #7189
• Add benchmark for set equality #7262
• Add benchmark for set equality #7262
• Add benchmark for exponential histogram measurements #7305
• Don't track min and max when disabled #7306
• Add concurrent safe tests for metric aggregations #7379
• Use RWLocks for counter measurements #7380
• Add measure benchmarks with exemplars recorded #7406
• Add benchmark for synchronous gauge measurement #7407
• Only enforce cardinality limits when the attribute set does not already exist #7422
• Allow optimizing locking for built-in exemplar reservoirs  #7423
• Use sync.Map and atomics to improve sum performance #7427
• Add exemplar reservoir parallel benchmarks #7441
• Optimize histogram reservoir #7443
• Document the ordering guarantees provided by the metrics SDK #7453
• PoC: HistogramReservoir uses a time-weighted algorithm #7458
• Use sync.Map and atomics for fixed bucket histograms #7474
• Use sync.Map and atomics for lastvalue aggregations #7478
• Exponential histogram: defer computing count until collect #7702
• PoC: allow reservoirs to defer recording the timestamp until storage #7711
• prototype for cumulative per-timeseries start timestamp #7719
• PoC: Metric instruments support an WithOptIn option. #7721
• PoC for bound entities in the trace SDK #7723
• PoC: Add AddWithAttributes to metrics api #7770
• PoC: metric.WithAttributes is now somewhat performant for dynamic attributes #7777
• PoC: Add AttributesDistinct to metrics API Config #7782
• Write a blog post highlighting changes and communicate performance gains