[bug]: `getSignerAndReqBody` OOMs on `Buffer` bodies (misuses object-only `isEmpty`)

Package: oci-common · affects any operation sending a binary Buffer request body of more than a few MB (e.g. ObjectStorage.putObject, UploadManager single-part uploads).

helper.ts#L223 checks the body with isEmpty() before the string/Readable type branches below it:

if (!body || isEmpty(body)) { ... }   // isEmpty = Object.keys(obj).length === 0

But isEmpty is documented for plain objects. When body is a Buffer (Uint8Array), Object.keys(body) materializes a string for every byte index — a ~20 MB body allocates ~20M strings synchronously → FATAL ERROR: Reached heap limit.

Crash stack:

Runtime_ObjectKeys → KeyAccumulator::GetKeys → TypedElementsAccessor::PrependElementIndices → SmiToString → OOMErrorHandler

Environment: container limited to 512 MB (V8 auto-sizes its heap to the cgroup limit), so the index-string burst exhausts the heap well before the body finishes enumerating.

Repro: putObject with a Buffer body of ~20 MB (or any UploadManager upload of a file at/below partSize, which is buffered into a single Buffer).

Fix: don't run the object-only isEmpty on a body — do the type-aware checks first (empty via .length/.byteLength for string/Buffer, and handle Buffer/ArrayBuffer.isView explicitly).

Start at lib/common/lib/helper.ts line 223 and read lib/common/lib/utils.ts lines 18-21 to understand the object-only isEmpty check. Reproduce the issue with ObjectStorage.putObject or an UploadManager single-part upload using a large Buffer, then verify type-aware body checks avoid the heap exhaustion and preserve empty-body handling.