Simple S3 client (#836)

This functionality is intended to be used to manage datasets for test cases, but may be useful elsewhere in the future.

- **Add S3 client with AWS Signature V4 (SigV4) signing** — new `S3Client` in `zenutil/cloud/` supporting `GetObject`, `PutObject`, `DeleteObject`, `HeadObject`, and `ListObjects` operations
- **Add EC2 IMDS credential provider** — automatically fetches and refreshes temporary AWS credentials from the EC2 Instance Metadata Service (IMDSv2) for use by the S3 client
- **Add SigV4 signing library** — standalone implementation of AWS Signature Version 4 request signing (headers and query-string presigning)
- **Add path-style addressing support** — enables compatibility with S3-compatible stores like MinIO (in addition to virtual-hosted style)
- **Add S3 integration tests** — includes a `MinioProcess` test helper that spins up a local MinIO server, plus integration tests exercising the S3 client end-to-end
- **Add S3-backed `HttpObjectStoreService` tests** — integration tests verifying the zenserver object store works against an S3 backend
- **Refactor mock IMDS into `zenutil/cloud/`** — moved and generalized the mock IMDS server from `zencompute` so it can be reused by both compute and S3 credential tests

1 files changed, 1 insertions, 17 deletions

diff --git a/src/zencompute/cloudmetadata.cpp b/src/zencompute/cloudmetadata.cpp
index 65bac895f..eb4c05f9f 100644
--- a/src/zencompute/cloudmetadata.cpp
+++ b/src/zencompute/cloudmetadata.cpp
@@ -23,22 +23,6 @@ static constexpr std::string_view kImdsEndpoint = "http://169.254.169.254";
 // is a local service on the hypervisor so 200ms is generous for actual cloud VMs.
 static constexpr auto kImdsTimeout = std::chrono::milliseconds{200};
 
-std::string_view
-ToString(CloudProvider Provider)
-{
-	switch (Provider)
-	{
-		case CloudProvider::AWS:
-			return "AWS";
-		case CloudProvider::Azure:
-			return "Azure";
-		case CloudProvider::GCP:
-			return "GCP";
-		default:
-			return "None";
-	}
-}
-
 CloudMetadata::CloudMetadata(std::filesystem::path DataDir) : CloudMetadata(std::move(DataDir), std::string(kImdsEndpoint))
 {
 }
@@ -610,7 +594,7 @@ CloudMetadata::PollGCPTermination()
 
 #if ZEN_WITH_TESTS
 
-#	include <zencompute/mockimds.h>
+#	include <zenutil/cloud/mockimds.h>
 
 #	include <zencore/filesystem.h>
 #	include <zencore/testing.h>