fix: align memory stress tests with backpressure behavior

- Make BACKPRESSURE_TIMEOUT configurable via S3PROXY_BACKPRESSURE_TIMEOUT env var
- Replace test_concurrent_uploads_bounded with test_backpressure_queues_concurrent_uploads
  (tests that queued requests succeed instead of asserting immediate 503)
- Replace test_rejection_is_fast_no_body_read with test_rejection_after_backpressure_timeout
  (uses 1s timeout to actually trigger rejections)
- Remove retries>0 assertions from memory-bounded tests (backpressure queues
  requests instead of rejecting, so retries don't happen with 30s timeout)

Author: ServerSideHannes

s3proxy/concurrency.py

@@ -42,7 +42,7 @@ def _create_malloc_release() -> Callable[[], int] | None:
 _malloc_release = _create_malloc_release()
 
 
-BACKPRESSURE_TIMEOUT = 30  # seconds to wait before rejecting
+BACKPRESSURE_TIMEOUT = int(os.environ.get("S3PROXY_BACKPRESSURE_TIMEOUT", "30"))
 
 
 class ConcurrencyLimiter: