WIP: start proto/gRPC support

[alexeagle]

/cc @acozzette

[alexeagle]

Not particularly close to working yet. I'm using the new uv machinery and I think it doesn't produce a package that works with py_console_script_binary so I'm not sure how to execute the grpcio_tools package which contains the grpc codegen.

[aspect-workflows]

Bazel 8 (Test)

⚠️ Buildkite build #2643 failed.

//py/unstable:defs.doc_extract failed to build

in deps attribute of starlark_doc_extract rule //py/unstable:defs.doc_extract: missing bzl_library targets
for Starlark module(s) //py/private:proto.bzl. Since this rule was created by the macro 'bzl_library', the
error might have been caused by the macro implementation

//py:defs.doc_extract failed to build

in deps attribute of starlark_doc_extract rule //py:defs.doc_extract: missing bzl_library targets for
Starlark module(s) //py/private:proto.bzl. Since this rule was created by the macro 'bzl_library', the error
might have been caused by the macro implementation

💡 To reproduce the build failures, run

bazel build //py/unstable:defs.doc_extract //py:defs.doc_extract

---

Bazel 9 (Test)

⚠️ Buildkite build #2643 failed.

//py:defs.doc_extract failed to build

in deps attribute of starlark_doc_extract rule //py:defs.doc_extract: missing bzl_library targets for
Starlark module(s) //py/private:proto.bzl. Since this rule was created by the macro 'bzl_library', the error
might have been caused by the macro implementation

//py/unstable:defs.doc_extract failed to build

in deps attribute of starlark_doc_extract rule //py/unstable:defs.doc_extract: missing bzl_library targets
for Starlark module(s) //py/private:proto.bzl. Since this rule was created by the macro 'bzl_library', the
error might have been caused by the macro implementation

💡 To reproduce the build failures, run

bazel build //py:defs.doc_extract //py/unstable:defs.doc_extract

---

Bazel 8 (Test)

e2e

All tests were cache hits

14 tests (100.0%) were fully cached saving 12s.

---

Bazel 9 (Test)

e2e

All tests were cache hits

12 tests (100.0%) were fully cached saving 7s.

---

Bazel 8 (Test)

examples/uv_pip_compile

All tests were cache hits

1 test (100.0%) was fully cached saving 335ms.

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