updated dockerfile manylinux

[HarishPermal]

This PR is focused on making the manylinux wheel build reproducible and more resilient in a minimal environment, while making Python imports degrade gracefully when optional native/task components are missing. It also switches OpenCV to static linking for wheels and disables GenAI converter targets that are likely unavailable in the build environment

1. Dockerfile.manylinux_2_28_x86_64

• Java 11 -> Java 21 and explicit JAVA_HOME: aligns with newer Bazel/JDK expectations and avoids build issues on newer toolchains.
• Bazel install switched from source build to prebuilt binary: speeds up the container build and reduces build-time dependencies.
• Added GCC toolset 14 include/lib paths and Bazel link opts: needed for C++20 std::span support and newer libstdc++ in manylinux.
• Protobuf protoc version bumped to 28.3: aligns with newer protobuf expectations in the build.
  *OpenCV build excludes opencv_apps: trims build time and avoids extra deps.
• .bazelrc gets explicit toolchain/linker env to ensure Bazel uses the newer libstdc++.
• Patch for OpenCV dependency reduction now optional via MEDIAPIPE_PYTHON_BUILD_DIFF_URL: lets the Docker build continue even if the diff isn’t present.
• GenAI converter targets removed and ENABLE_ODML_CONVERTER=0: avoids building GenAI converter components not needed for wheel build or missing deps.

2. build_manylinux_wheel.sh

• New helper script to build the manylinux image and extract wheel(s) to ./wheelhouse. This is a convenience wrapper for the container build and wheel extraction.

3. third_party/BUILD

• OPENCV_SHARED_LIBS = False: forces static OpenCV linking, which is preferred for manylinux wheels to reduce runtime shared library dependencies.

4. mediapipe/tasks/c/BUILD

• Removes GenAI C library dependencies from the C tasks binary: matches the Dockerfile’s decision to disable GenAI converter targets.

5. setup.py

• Version is now read from version.bzl, removing the old "dev" hardcode.
• The old behavior that appended task imports to __init__.py is removed.

6. metadata.py

• Handles missing native metadata bindings (_pywrap_metadata_version) with a clear error when metadata export is attempted. This avoids hard crashes during import.