feat(ext/cache): inject W3C traceparent/tracestate into LSC HTTP requests

[wperron]

Extract the active trace context on the JS side using the telemetry propagators (ContextManager.active() + PROPAGATORS.inject()) and pass the traceparent and tracestate values as optional string fields through the cache op calls (op_cache_put, op_cache_match, op_cache_delete).

On the Rust side, CacheShard::get_object, put_object, and put_object_empty now accept an optional trace_headers parameter and inject the corresponding HTTP headers into outgoing LSC requests, enabling distributed trace propagation through the cache layer.

[kajukitli]

looks fine overall, but i think this needs a test before merging

right now the JS side is extracting active trace context and threading traceparent / tracestate through the cache ops into LSC requests, but there's no coverage proving those headers actually make it onto the outgoing HTTP calls.

without a test this is pretty easy to regress later because the propagation path crosses a lot of layers:
01_cache.js -> op structs -> lsc backend -> shard request building

suggestion: add an integration test with tracing enabled and a fake LSC endpoint that records request headers, then assert traceparent is present on:

• cache.put()
• cache.match()
• cache.delete()

and ideally also assert tracestate is forwarded when set.