Simplify .gitattributes handling for C/C++ headers

[rwgk]

Summary

This simplifies the .gitattributes handling for checked-in .h and .hpp files.

Plain git diff now works intuitively across the tracked source headers, so changes in these files appear as normal text diffs without requiring git diff -a. This should also make future header additions less surprising. A newly added .h or .hpp file will behave like normal source by default, instead of silently becoming binary-classified unless someone remembers to add a matching exception rule.

The old attributes treated every C/C++ header as binary, then carved out path-specific exceptions for headers maintained in this repository. That was based on an outdated assumption that checked-in headers were broadly generated or hands-off inputs.

The tracked header set is much smaller and clearer: the only header that needs Git-level byte preservation is the vendored DLPack header. This change keeps cuda_core/cuda/core/_include/dlpack.h opted out of Git text normalization with -text and an explicit !eol reset, while forcing text diffs so review output stays readable.

All other tracked headers now inherit the repository default text eol=lf behavior, consistent with Python files and other normal source. This includes repo-owned C++ helpers as well as the AOTI shim adaptation, which is third-party-derived but maintained here rather than a byte-for-byte vendored header.

Fresh Clone Behavior

For a fresh clone, this should not change the bytes of the nine existing tracked headers on Linux or Windows. The blobs are already stored with LF line endings.

On main, exception headers checked out as LF via text eol=lf, while the remaining binary-classified headers were written as raw LF blob bytes. After this change, ordinary headers still check out as LF via text eol=lf, and DLPack remains raw LF.

For a fresh clone, the only observable change is Git behavior: ordinary headers stop being binary-classified, and DLPack remains no-normalization but becomes text-diffable.

Pre-commit

Pre-commit behavior is unchanged and still governed by hook-specific matching.

Validation

Checked the effective attributes with git check-attr and verified the tracked header line-ending state with git ls-files --eol.

Details

This change affects the attributes for the nine tracked .h and .hpp files.

These five files were already treated as text on main by path-specific exception rules that overrode the broad binary header rule with -binary text diff:

benchmarks/cuda_bindings/benchmarks/cpp/bench_support.hpp
cuda_bindings/cuda/bindings/_bindings/loader.h
cuda_bindings/cuda/bindings/_lib/param_packer.h
cuda_core/cuda/core/_cpp/resource_handles.hpp
cuda_core/cuda/core/_cpp/tensor_map_cccl.h

These three files were binary-classified on main, but are maintained source in this repository and should inherit the same text eol=lf behavior as other normal source files:

cuda_core/cuda/core/_include/aoti_shim.h
cuda_core/cuda/core/_include/layout.hpp
cuda_core/cuda/core/_include/utility.hpp

This one file remains special-cased because it is the byte-for-byte vendored header that should not be normalized by Git:

cuda_core/cuda/core/_include/dlpack.h

[rwgk]

Running the full CI for this out of an abundance of caution, in case there are any unexpected git clone surprises.

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