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, 0 deletions

diff --git a/src/zenutil/xmake.lua b/src/zenutil/xmake.lua
index 1d5be5977..1e19f7b2f 100644
--- a/src/zenutil/xmake.lua
+++ b/src/zenutil/xmake.lua
@@ -9,6 +9,7 @@ target('zenutil')
     add_deps("zencore", "zenhttp")
     add_deps("cxxopts")
     add_deps("robin-map")
+    add_packages("json11")
 
     if is_plat("linux") then
         add_includedirs("$(projectdir)/thirdparty/systemd/include")