Streaming copy example with aiohttp

Add example to docs of passing streaming download from aiohttp into streaming multipart upload

Ref https://github.com/developmentseed/obstore/issues/398#issuecomment-2766564086

```py
from aiohttp import ClientSession
from boto3.session import Session

from obstore.auth.boto3 import Boto3CredentialProvider
from obstore.store import S3Store

s = Session(profile_name="ds")
cp = Boto3CredentialProvider(Session(profile_name="ds"))
store = S3Store("bucket", credential_provider=cp, region="us-east-1")

url = "https://storage.googleapis.com/open-geodata/linz-examples/nz-buildings-outlines.parquet"

async with ClientSession() as session, session.get(url) as resp:
await store.put_async("test_upload.parquet", resp.content.iter_any())
```

Locate the documentation examples and start from the async upload entry point, store.put_async, alongside aiohttp's resp.content.iter_any(). Add the requested streaming download-to-multipart-upload example using the shown setup, and consider the work done when the example is present and readable in the docs.

Written by the indexing model from the issue text.