fix: Redact anonymous context attributes in server-side custom events

[keelerm84]

Summary

The C++ event processor emitted custom (track) events using the non-redacting context filter, so anonymous contexts were sent with all attributes intact. Server-side SDKs now redact all attributes of anonymous contexts in custom events (matching feature-event behavior); client-side SDKs continue to send them unredacted (they redact anonymous attributes only in feature events).

• Gated the custom-event context filter on the SDK template type in AsioEventProcessor<SDK>::Process: FilterWithAnonymousRedaction for the server SDK, Filter for the client SDK.
• Mirrors the redactAnonymousAllEvents split in java-core / dotnet-core.
• Verified against the sdk-test-harness v3 custom-event tests: server redacts, client does not.

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Note

Medium Risk
Changes what PII/context data leaves server-side custom events (privacy fix), but scope is limited to one code path and mirrors existing feature-event filtering.

Overview
Server-side custom (track) events now run context through FilterWithAnonymousRedaction before emission, so anonymous contexts no longer ship with full attributes in those payloads. Client SDK track events still use the standard Filter path, unchanged.

The branch is chosen in AsioEventProcessor<SDK>::Process from the SDK template type, aligning track events with how full feature events already redact anonymous context on the server and with redactAnonymousAllEvents behavior in other SDKs.

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