stripNonEssentialElements

Strip non-essential CoT detail before mesh compression to save wire bytes. Delegates (via the CotSanitizer expect/actual seam) to the SDK's CotMeshSanitizer so the strip rules live in ONE golden-tested place shared by every consumer (Android, Apple, …) and can't drift between sides. Drift here once silently stripped TAK-Talk <voice> / <marti> and broke the feature end-to-end — guarded by the strip-preservation test in TAKMeshIntegrationTest and by CotMeshSanitizerTest in the SDK.