Protobuf 7.35.1+ support

`google-cloud-aiplatform` pins `protobuf<7.0.0`, but `grpcio-tools>=1.83.0` requires `protobuf>=7.35.1`. These two ranges don't overlap, so this package can't be installed alongside a current `grpcio-tools`.

Checked via `pip download --no-deps` and reading `METADATA`:

- `google-cloud-aiplatform==2.1.0`: `protobuf!=4.21.0,...,!=4.21.5,<7.0.0,>=3.20.2`
- `grpcio-tools==1.83.0`: `protobuf<8.0.0,>=7.35.1`, `grpcio>=1.83.0`

Also, source:
- [`google-cloud-aiplatform setup.py` @ v2.1.0](https://github.com/googleapis/python-aiplatform/blob/v2.1.0/setup.py#L328): `protobuf>=3.20.2,<7.0.0,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5`
- [`grpcio-tools tools/distrib/python/grpcio_tools/setup.py`@v1.83.0](https://github.com/grpc/grpc/blob/v1.83.0/tools/distrib/python/grpcio_tools/setup.py#L340): `protobuf>=7.35.1,<8.0.0`

gRPC only supports the current release and the one before it ([FAQ](https://grpc.io/docs/what-is-grpc/faq/#how-long-are-grpc-releases-supported-for)), and ships roughly every 6 weeks. 1.83.0 came out 2026-07-21, so the next release will drop support for everything below it — at that point there's no supported `grpcio` left that's compatible with this cap.

Can you bump the protobuf upper bound (`<8.0.0` would match grpcio-tools) so the package stays installable with a supported gRPC
version?
Thanks!

Start with google-cloud-aiplatform setup.py at the dependency declaration cited in the issue, then compare it with grpcio-tools 1.83.0 metadata. Verify the updated range using pip download and confirm that the package can be installed alongside a supported grpcio-tools release.

索引モデルが issue の本文から書いたものです。