Add CCKR adaptive log reservoir sampler to Microsoft.Extensions.Telem…

[evgenyfedorov2]

…etry

Implements the CCKR (Chao-Cohen-Kaplan-Reservoir) adaptive log sampler as implementations of the existing LoggingSampler and LogBuffer seams, so no changes to the logging pipeline are required:

• Cckr<TCallsite,TPayload>: bottom-(K+1) weighted reservoir with EXP ranks, cross-period inverse-frequency feedback, Chao1 unseen-weight, bounded novelty preserve, and Horvitz-Thompson sampling weights (faithful port of the reference algorithm).

• CckrLoggingSampler (LoggingSampler): the admit/drop decision. CckrLogBuffer (LogBuffer): holds admitted records per category and emits the kept records carrying the sampling.count weight at each flush, reusing SerializedLogRecord/DeserializedLogRecord/IBufferedLogger.

• AddCckrLogSampling registers one reservoir instance as both seams. Public API: AddCckrLogSampling, ReservoirSamplingConfig, UnseenWeightMode.

Microsoft Reviewers: Open in CodeFlow

[Yun-Ting]

Suggested change

	if (_heap.Count > _reservoirCapacity)
	// Retain T+1 entries: the root is the (K+1)-th smallest rank, the first item excluded from the bottom-K sample (tau)
	if (_heap.Count > _reservoirCapacity + 1)

In Bottom (K + 1) algorithm, tau is the rank of the first excluded item.
That's what keeps tau independent of every retained item's own rank; the condition the HT weights to be correct.

[Yun-Ting]

Suggested change

	double finalTau = Tau;
	// tau is the (K+1)-th smallest rank (the first excluded item), so take it from the heap before draining. i.e.: leaving exactly K records to emit.
	double finalTau = double.PostiveInfinity;
	if (_heap.Count > _reservoirCapcity)
	{
	finalTau = HeapPopMax().Key;
	}

[Yun-Ting]

question - do we need to call Flush() here before disposing, so we don't lose whatever's still in the reservoirs up to a full FlushInterval?

I don't think the providers are gone by this point. And ExtendedLoggerFactory.cs:76 registers DI-supplied providers with dispose: false, so the factory skips them and the container disposes them itself (in reverse creation order.)