[Sushisource]

What was changed

• Add default-false ContextPropagator.encodeHeaders() and OpenTracing/OpenTelemetry options using the configured client's payload codec, compatible with existing propagator implementations.
• Encode only opted-in producers' output, leaving application-supplied wire-ready headers unchanged. Opted-in inbound consumers receive decoded copies; tracing keeps standard serialization. Encoding ownership follows the producer’s key and payload instance.
• Preserve destination contexts, header presence, raw schedule retention, storage ordering, and once-only multioperation processing, without converter policy wrappers or a separate header-only codec chain.

Breaking changes: None. Existing producers default to false; custom converter wrappers can forward PayloadCodecProvider to expose their codec.
Server PR: Not required.

Why?

Part of temporalio/features#850. Tracing and context propagators can opt into the configured client codec without double-encoding unrelated user-supplied headers or changing existing defaults.

Checklist

1. Related issue: Normalize Header Data Conversion across languages features#850 (this PR does not close the cross-SDK issue).
2. How was this tested:
   • Mixed producers, plaintext/pre-encoded header isolation, contextual binding, and codec errors/cardinality.
   • Client/worker boundaries, tracing, storage, retained schedules, child namespaces, reused multioperation headers, and activity/Nexus client propagation. Targeted Gradle suites and Spotless passed using scratch protobuf sources from the exact pinned API commits because local submodules are partial; one existing memo test was skipped. Full suites and remote CI were not verified.
3. Any docs updates needed? README, public API documentation, and changelog included; guidance covers producer opt-in, configured-client codecs, compatible decoders, and wrapper forwarding.