Upgrade Struct2Tensor to TensorFlow 2.21.0

[vkarampudi]

This PR upgrades struct2tensor to support TensorFlow 2.21.0 and resolves various build system incompatibilities, dependency conflicts, and compilation errors encountered during the process.

Key Changes

1. TensorFlow & Bazel Version Alignment

   • Updated .bazelversion to 7.7.0 to align with TensorFlow 2.21.0 requirements.
   • Updated WORKSPACE to fetch TensorFlow 2.21.0

2. Dependency Management & Bzlmod

   • Disabled Bzlmod: Added common --noenable_bzlmod to .bazelrc. This was necessary to resolve severe version mismatch issues with Protobuf when using Bazel 7, ensuring we use the versions specified in WORKSPACE.
   • Updated PyArrow: Updated pyarrow dependency in setup.py to >=14 to resolve security vulnerabilities and ensure compatibility.

3. Build System Workarounds (Dummy Repositories)

   • TensorFlow 2.21.0 introduced complex external dependency chains that caused circular dependencies or expected configurations (like CUDA/ROCm) that are not present in this project.
   • To bypass these, I created several "dummy" repositories in third_party/ and registered them in WORKSPACE:
     • rules_java: A minimal dummy repo to satisfy Java dependencies without pulling in heavy external rules.
     • local_config_cuda, local_config_rocm, local_config_tensorrt, local_config_sycl: Dummy repositories to satisfy TensorFlow's GPU configuration checks without requiring actual GPU setups.

4. Compiler & Linker Fixes

   • Enforced C++17: Added flags to .bazelrc to ensure C++17 is used globally, as required by newer Abseil and TensorFlow headers.
   • Protobuf Patch: Added third_party/protobuf_retain_options.patch to remove the --retain_options flag from Protobuf generation rules, which was causing failures with the version of protoc used in Bazel 7.
   • Missing Includes: Added #include <cstdint> to several C++ files in struct2tensor/ops/ and struct2tensor/kernels/ to fix missing uintptr_t definitions when compiling with newer compilers (like gcc 15).
   • SFrame Flag (Attempted & Removed): I initially added --copt=-Wa,--gsframe=no to .bazelrc to fix a relocation error specific to gcc 15. However, this caused the PR build to fail because the PR runner's assembler did not support that flag. I have removed it for PR compatibility. If you build locally with gcc 15 and see relocation errors, you may need to pass it manually.

5. Test Suite Execution

   • Sharding Check Disabled: Passed --noincompatible_check_sharding_support to bazel test to bypass sharding support checks that were failing in benchmark tests.

Verification

All tests passed successfully locally:

bazel test //... --noincompatible_check_sharding_support ...