Feat/add vmaf

[mockodin]

Summary

Add VMAF 3.2.0 to the bundled FFmpeg builds and enable FFmpeg's libvmaf filter across supported native and cross-compiled platforms.

The build now verifies both the packaged VMAF runtime library and the ability to locate and initialize the libvmaf filter.

Implementation Details

• Add VMAF 3.2.0 to the codec dependency group.
  • Verify the source archive with a pinned SHA-256 digest.
  • Build libvmaf as a shared library with Meson.
  • Disable VMAF tests, documentation, and command-line tools.
• Configure FFmpeg with --enable-libvmaf.
• Validate every generated archive before accepting or reusing it.
  • Windows: require bin/libvmaf.dll.
  • macOS: require a non-empty lib/libvmaf.*.dylib.
  • Linux: require a non-empty versioned lib/libvmaf.so.*.
• Extend the existing package import smoke test.
  • Locate the libvmaf filter with avfilter_get_by_name.
  • Create a filter graph and initialize the filter.
  • Raise a Python exception when lookup, allocation, or initialization fails.
  • Keep verification isolated in verify_libvmaf_filter().
  • Preserve the existing FFmpeg is OK success output.
• Provision a compatible xxd implementation for VMAF model embedding.
  • Test the exact xxd -i INPUT OUTPUT invocation VMAF requires.
  • Reject incompatible implementations that cannot write to an output file.
  • Install xxd through the available Linux package manager when needed.
  • Install vim in MSYS2 builds to provide xxd on Windows.
• Run the host-tool setup before native Linux, manylinux, and musllinux builds.
• Fail artifact upload steps when a build produces no output.
• Document VMAF 3.2.0 in the enabled dependency list.

Testing Done

• Full GitHub Actions build matrix passed for the VMAF integration:
  • macOS arm64 and x86_64
  • Linux aarch64 and x86_64
  • Windows ARM64 and x86_64
  • manylinux armv7l, ppc64le, and riscv64
  • musllinux armv7l, ppc64le, and riscv64
• Reproduced the musllinux environment and verified replacement of an incompatible xxd implementation.
• Confirmed generated archives contain a non-empty platform-specific VMAF runtime library.
• Confirmed the packaged FFmpeg build exposes and initializes the libvmaf filter.
• Strict C syntax and type checking passed after extracting verify_libvmaf_filter().
• git diff --check passed.

[WyattBlue]

d7a92d1

[mockodin]

Closing, I was late in posting and missed that @WyattBlue got there first :)
#253