fix: oversize payload causing universal instrumentation failures

[joeyzhao2018]

Instead of passing the whole Request into the spawned task and calling extract_request_body (which consumes the request and early-returns on failure), the fix:

1. Splits the request upfront with request.into_parts() — headers are preserved regardless of body extraction outcome
2. Attempts body buffering via Bytes::from_request
3. Falls back to Bytes::new() on failure (e.g. oversized payload) with a warn! log
4. Always calls universal_instrumentation_end — trace context, span finalization, and status code extraction proceed with degraded (empty) payload rather than being silently
   dropped

The FromRequest import was added to the module-level axum imports to support calling Bytes::from_request directly.

[duncanista]

So if you're using extract_request_body_or_empty, what's going on with extract_request_body? Is that ever used again? Do we need to update this new behavior in previous usages or?

[joeyzhao2018]

there are a few other usages for extract_request_body

1. datadog-lambda-extension/bottlecap/src/extension/telemetry/listener.rs

   Line 97 in dda9b26

   let (_, body) = match extract_request_body(request).await {

2. datadog-lambda-extension/bottlecap/src/otlp/agent.rs

   Line 144 in dda9b26

   let (parts, body) = match extract_request_body(request).await {

3. datadog-lambda-extension/bottlecap/src/traces/stats_processor.rs

   Line 45 in dda9b26

   let (parts, body) = match extract_request_body(req).await {

4. datadog-lambda-extension/bottlecap/src/traces/trace_agent.rs

   Line 479 in dda9b26

   let (parts, body) = match extract_request_body(request).await {

5. datadog-lambda-extension/bottlecap/src/traces/trace_agent.rs

   Line 659 in dda9b26

   let (parts, body) = match extract_request_body(request).await {

I actually don't have enough background knowledge to say if those cases can follow the same pattern...Do you think we should make all of them just log the error and accept empty body?

[duncanista]

I see, fair enough, let's keep it as is for this one and let the other ones handle it as they expect it

[duncanista]

LGTM