[proto tooling] add hermetic protoc compilation managed by bazel

[albertywu]

Summary

Bazel-ify the entire codegen toolchain so a single make proto produces byte-identical output on any host.

Previously, make proto was dependent on host-installed versions of protoc + plugins which led to different output when run on different machine.

Test Plan

✅ make fmt && make proto && make build && make test && make e2e-test
✅ make proto <-- no changes to generated source
✅ Modify .proto -> call make proto -> see expected updates to all protopb/* files

Issues

T3-CODE-204

[Copilot]

Pull request overview

Adds Bazel-managed, hermetic protobuf compilation for the repo’s Go/YARPC stubs, and updates developer workflows to use Bazel as the protoc + plugin source of truth.

Changes:

• Introduces a custom Starlark rule (go_proto_generated_files) that runs protoc from the registered proto toolchain with pinned Go/gRPC/YARPC plugins.
• Adds Bazel targets under //tool/proto to generate the repo’s gateway/orchestrator protos for both submitqueue and stovepipe.
• Updates make proto (and docs) to generate via Bazel and copy results back into the checked-in */protopb directories.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tool/proto/proto_codegen.bzl	New Starlark rule wrapping hermetic protoc execution for Go/grpc/yarpc outputs.
tool/proto/BUILD.bazel	Adds concrete generation targets for the four existing proto entrypoints and a generated filegroup.
submitqueue/orchestrator/proto/BUILD.bazel	Exports orchestrator.proto to allow //tool/proto to depend on the source file directly.
submitqueue/gateway/proto/BUILD.bazel	Exports gateway.proto to allow //tool/proto to depend on the source file directly.
stovepipe/orchestrator/proto/BUILD.bazel	Exports orchestrator.proto to allow //tool/proto to depend on the source file directly.
stovepipe/gateway/proto/BUILD.bazel	Exports gateway.proto to allow //tool/proto to depend on the source file directly.
MODULE.bazel	Pins a toolchains_protoc protoc version and adds a bzlmod Go module entry to obtain protoc-gen-go-grpc.
Makefile	Replaces direct protoc invocations with bazel build //tool/proto:generated + copy-back + goimports formatting.
doc/howto/DEVELOPMENT.md	Updates local setup + troubleshooting to reflect Bazel-provided protoc/plugins rather than local installs.

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