fix: close async blob files after interrupted uploads

[po-et]

When an async blob upload fails while its input generator is suspended, AsyncClient.create_blob() can return the exception while the local upload file is still open. This also occurs on task or AnyIO cancel-scope cancellation.

Make the awaited upload own the file and close it in finally. Shield only the close operation so cancellation cannot interrupt cleanup; the original failure or cancellation still propagates.

Three regressions use a real temporary file and a synthetic HTTPX transport: WriteError, actual asyncio task cancellation, and AnyIO cancel-scope cancellation. All three fail against the current implementation and pass with the fix. A successful 65,537-byte upload also retains the correct payload, digest and closed file handles.

Validation on Python 3.12/macOS:

.venv/bin/python -m pytest ollama tests -q
.venv/bin/ruff check ollama tests
.venv/bin/ruff format --check ollama tests
git diff --check

123 tests passed; lint and formatting passed. No model or Ollama server is needed. The broader Python/OS matrix, including Python 3.8 runtime compatibility, remains for CI.

Prepared with AI assistance and independently reviewed against the actual source and local runtime; no human pre-review is claimed.