S3 suffix-range GET on a zero-byte object returns private NotPartial wrapped as Error::Generic

**Describe the bug**

Requesting a suffix range from an existing zero-byte S3 object fails with `Error::Generic(GetResultError::NotPartial)`. S3 returns a 200 for the suffix-range GET when the object is 0 bytes, but object_store expects a 206.

**To Reproduce**

```rust
let options =
GetOptions::new().with_range(Some(GetRange::Suffix(512 * 1024)));
let result = store.get_opts(&path, options).await;
```

For a zero-byte object, AWS S3 responds with:

```
HTTP/1.1 200 OK
Content-Length: 0
```

**Expected behavior**
Either the call should return success, or fail with some error with a specific type that the caller can use to discriminate and handle this case specifically (e.g. by falling back to a HEAD).

Start by reproducing get_opts with GetOptions and GetRange::Suffix against an existing zero-byte S3 object, then trace how the 200 response becomes Error::Generic(GetResultError::NotPartial). Confirm the intended behavior with maintainers, add coverage for this response, and ensure callers can distinguish or successfully handle the zero-byte case.

Written by the indexing model from the issue text.