* test: add self-contained S3 read/write load tool
Concurrent PUT/GET against the S3 gateway, reporting requests/sec,
transfer rate, and latency percentiles. Built on the aws-sdk-go-v2
client the S3 tests already use, so no extra benchmark binary is needed.
* ci: add performance workflow
Three parallel jobs: cpu/heap pprof of the server under write load,
native throughput via weed benchmark plus the Go micro-benchmarks, and
an S3 read/write benchmark against the gateway. Runs on push to master
and manual dispatch with tunable duration, object count, size, and
concurrency.