Async generator crash fixed; LLM span writer timeout honored

Bug Fixes

• tracing: Resolves an issue where wrapping an async generator on Python 3.11 through 3.14 raises a TypeError: object NoneType can't be used in 'await' expression error. This occurs when the generator body awaits a coroutine that suspends to the event loop before its first yield. Python 3.9 and 3.10 are not affected.

• LLM Observability: Fixes an issue where the span writer ignored its configured request timeout (_DD_LLMOBS_WRITER_TIMEOUT, default 5 seconds) and instead used the 2 second connection default, causing intermittent TimeoutError and dropped span events on high-latency connections to the agent or intake.