feat: support Protobuf Editions (2023/2024) and modernize build toolchain

[Kybxd]

Related to tableauio/tableau#370

Summary

This PR enables Protobuf Editions support across all three code generators
(Go / C++ / C#), upgrades the build toolchain, and makes the protobuf submodule
build pipeline version-aware so that both legacy protobuf v3.x and modern
v4+ / v21+ / v32+ releases can be used interchangeably.

Motivation

• Protobuf Editions (starting from Edition 2023) is the successor of proto2
  and proto3. Downstream users moving to Editions-based .proto files need
  their protoc plugins to advertise FEATURE_SUPPORTS_EDITIONS, otherwise
  code generation fails.
• The vendored protobuf submodule was previously pinned to a v3.x layout
  (cmake/ subdirectory, no cmake --install step). Modern protobuf releases
  moved CMakeLists.txt to the repo root and rely on protobuf-config.cmake
  generated via cmake --install, so our init scripts and downstream
  CMakeLists.txt needed to be updated.
• The Go toolchain / google.golang.org/protobuf runtime had to be bumped so
  that the Editions descriptor APIs (Edition_EDITION_PROTO2,
  Edition_EDITION_2024, SupportedEditionsMinimum/Maximum) are available.

Changes

Code generators: advertise Editions support

• cmd/protoc-gen-go-tableau-loader/main.go
• cmd/protoc-gen-cpp-tableau-loader/main.go
• cmd/protoc-gen-csharp-tableau-loader/main.go

Each plugin now sets:

gen.SupportedFeatures = uint64(
    pluginpb.CodeGeneratorResponse_FEATURE_PROTO3_OPTIONAL |
    pluginpb.CodeGeneratorResponse_FEATURE_SUPPORTS_EDITIONS,
)
gen.SupportedEditionsMinimum = descriptorpb.Edition_EDITION_PROTO2
gen.SupportedEditionsMaximum = descriptorpb.Edition_EDITION_2024

Toolchain upgrade

• go.mod: go 1.21 → go 1.24.0;
  google.golang.org/protobuf v1.34.2 → v1.36.11.
• Release / testing workflows: Go 1.21.x → 1.24.x.
• test/csharp-tableau-loader/Loader.csproj:
  Google.Protobuf 3.19.3 → 3.32.0.

Version-aware protobuf submodule build (init.sh / init.bat)

• Support a new PROTOBUF_REF env var to check out any protobuf tag before
  building (used by CI to matrix-test multiple protobuf versions).
• Auto-detect protobuf major version via git describe:
  • v3.x (legacy): build from the cmake/ subdirectory with the original
    minimal options.
  • v4+ / v21+ / v32+ (modern): build from the repo root with
    -Dutf8_range_ENABLE_INSTALL=ON.
• Switch build directory from build/ to .build/ (already in protobuf's
  .gitignore) to avoid dirtying the submodule working tree.
• Add a cmake --install .build --prefix .build/_install step so that
  protobuf-config.cmake, absl-*.cmake, and utf8_range-config.cmake are
  emitted for downstream find_package(Protobuf CONFIG) consumers.

Downstream CMake / docs alignment

• test/cpp-tableau-loader/CMakeLists.txt: look up protobuf under
  third_party/_submodules/protobuf/.build/_install (install tree) instead of
  the old in-source cmake/build tree.
• README.md: update dev instructions on Linux / Windows / C# to reflect the
  new .build/_install/bin layout for protoc / buf generate.

CI: multi-version protobuf matrix

• .github/workflows/testing-{go,cpp,csharp}.yml:
  • Add a protobuf-version matrix dimension: ["32.0", "3.19.3"], so each
    PR is validated against both the latest Editions-capable protobuf and the
    legacy v3.x line.
  • Wire PROTOBUF_REF=v${{ matrix.protobuf-version }} into the init script
    so the submodule is checked out at the matching tag before building.
  • Split Install Protoc into two steps: arduino/setup-protoc@v3 for
    modern versions, and the legacy @v1 action for the 3.x line.
  • Bump the C++ job timeout from 10 → 20 minutes to accommodate the modern
    protobuf build on Windows.

Compatibility

• No changes to generated code or runtime behavior for existing proto2 /
  proto3 users.
• Existing users who continue to use protobuf v3.19.x can keep doing so —
  the init scripts detect the version and fall back to the legacy layout.
• Users on protobuf v32+ / Editions 2023/2024 can now generate loader code
  without hitting feature not supported: EDITIONS errors.

Testing

• CI matrix: {ubuntu-latest, windows-latest} × {protobuf 32.0, protobuf 3.19.3}
  across Go / C++ / C# suites.
• Local smoke test on Linux with protobuf v32.0 submodule + Editions-based
  .proto inputs.

[wenchy]

For better compatibilty, keep v3.19.3 for commited source code. the new protoc generated code has more dependencies (e.g.: C++ absl).

We can test the new features with a feature gate option to enable/disable in the plugin params.

refer to https://github.com/tableauio/loader/blob/v0.5.0/cmd/protoc-gen-cpp-tableau-loader/main.go#L43

[Kybxd]

okay, our workflow guarantees the generated code works well with protobuf v32.0.