fix(kernels): initialize submodules during build

[Ma1oneZhang]

Summary

• initialize missing git submodules from openinfer-kernels/build.rs before CUDA feature generation or vendored header checks
• skip the update when git submodule status --recursive shows no uninitialized entries, so normal rebuilds do not touch the network
• keep explicit diagnostics if git inspection or initialization fails
• document the first-build new-user failure mode in docs/subsystems/kernels/build-rs-submodule-init.md

Tracking issue

• Closes Auto-initialize kernel submodules on first build #1

Verification

• cargo fmt --check
• OPENINFER_CUDA_SM=80 OPENINFER_NVCC_JOBS=1 cargo check -p openinfer-kernels --no-default-features

Upstream note

This PR is opened on the fork because the current GitHub token cannot create pull requests on openinfer-project/openinfer.