Add async raw S3 packet writes

[cliffburdick]

No description provided.

[greptile-apps]

Greptile Summary

This PR introduces DAQIRI_ENABLE_S3, an opt-in CMake feature that adds asynchronous raw packet uploads to Amazon S3 or any S3-compatible object store, backed by the AWS SDK for C++.

• New src/common_s3.cpp: a self-contained async S3 write path — per-packet PutObject pipeline with a mutex/condition-variable completion tracker, pinned-host staging buffers (cudaMallocHost), and a reference-counted AWS SDK lifecycle manager. Correct stub implementations are compiled when S3 is disabled.
• Public API additions in include/daqiri/common.h: S3WriterConfig, S3WriteStatus, opaque S3Writer/S3WriteHandle types, and six free functions (daqiri_s3_writer_create, daqiri_write_raw_to_s3_objects_async, poll/wait/destroy variants).
• Python bindings in python/daqiri_common_pybind.cpp: RAII PyS3Writer/PyS3WriteHandle wrappers with GIL-scoped release on all blocking calls, bound as daqiri.S3Writer and daqiri.S3WriteHandle.

Confidence Score: 5/5

Safe to merge. The S3 write path is additive and off by default; existing packet I/O paths are unaffected.

All three commits carry a DCO sign-off and use the required #124 - ... title format. The async completion logic (mutex, condition variable, inflight counter) is correct — daqiri_s3_write_wait holds the lock until done is set, preventing the handle from being deleted while callbacks are still live. Staging buffers use cudaMallocHost/cudaFreeHost correctly, release_memory() intentionally preserves size so that SetContentLength and the bytes_uploaded counter downstream remain accurate. The AWS SDK refcount is properly guarded. Python bindings release the GIL on every blocking call and the RAII destructors prevent double-free. Doc updates cover the new option. No burst-free violations, no backend-type branching in common code.

No files require special attention.

Important Files Changed

Filename	Overview
src/common_s3.cpp	New S3 write implementation — async PutObject pipeline with correct mutex/CV lifecycle, staging-buffer management, and AWS SDK refcount. Stub fns provided for disabled builds.
include/daqiri/common.h	Adds S3WriterConfig, S3WriteStatus, S3Writer/S3WriteHandle opaque types, and six new API functions. Follows existing BurstParams-free-contract conventions.
python/daqiri_common_pybind.cpp	Adds PyS3Writer/PyS3WriteHandle RAII wrappers with GIL-release on blocking calls; write_raw_objects correctly handles wait+destroy sequence without double-free.
src/CMakeLists.txt	Adds DAQIRI_ENABLE_S3 CMake option; common_s3.cpp unconditionally compiled with stub fns when disabled; socket→rdma invariant untouched.
Dockerfile	Builds AWS SDK for C++ S3-only from source; pinned version via AWS_SDK_CPP_VERSION ARG with sane defaults; SDK installed unconditionally in base image.
cmake/daqiriConfig.cmake.in	Correctly propagates DAQIRI_ENABLE_S3 and calls find_dependency(AWSSDK COMPONENTS s3) for downstream CMake consumers when S3 is enabled.

_{Reviews (4): Last reviewed commit: "#124 - Guard S3 helpers in disabled buil..." | Re-trigger Greptile}