feat: Keep override-affected evaluations out of individual events

[kinyoklion]

Summary

This PR is based on the override store branch because it consumes the override marking that branch produces on evaluation results.

This change adds the analytics event behavior of the OVERRIDE specification to the shared event code and the Node.js server SDK.

An evaluation marked as override-affected produces no individual feature event and no debug event, even when the flag requests them. It is still counted in summary events like any other evaluation, in a separate counter that carries the overrideAffected marker. The marker is part of the summary aggregation key, so override-affected and other evaluations of the same flag, variation, and version accumulate into separate counters rather than collapsing together. The marker is present on a counter only when true, like the existing unknown marker.

The client hands the marking to the event processor as a scalar on the input event, taken from the evaluation result. Event generation does not read the evaluation reason. The record of a prerequisite evaluation carries the prerequisite's own marking, so an unaffected prerequisite inside a marked top-level evaluation still produces its individual event, while a marked prerequisite record produces none and is counted under the marked counter for the prerequisite flag.

The shared event summarizer and processor are also used by the client-side SDKs. The new field is optional and those SDKs never set it, so their output is unchanged.

The OVERRIDE test vector runner now also asserts the marking of the summary counter that each evaluation contributes to, by flushing the events and reading the summary payload.

SDK-3247

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Note

Overview
Implements OVERRIDE-spec analytics behavior for evaluations affected by the override store.

Override-affected evaluations still roll into summary events, but no individual feature or debug events are emitted even when trackEvents / debug mode are on. Summaries use a separate counter bucket keyed by an optional overrideAffected: true marker (omitted when false, like unknown).

The server SDK passes evalRes.overrideAffected into event creation as a scalar—not derived from the evaluation reason. Prerequisite eval records use each prerequisite’s own marking, so unaffected siblings can still emit feature events while marked flags in the same tree only appear in marked summary counters.

Shared EventFactoryBase, InputEvalEvent, summarizer, and processor carry the new optional field; client SDKs that never set it are unchanged. Tests cover the shared pipeline, full client + override scenarios (including prereq trees), and OVERRIDE vector assertions for summaryOverrideAffected.

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