cuda.bindings: add decode_c_str helper for actionable UnicodeDecodeError (#2122)

[aryanputta]

Summary

Adds cuda.bindings._internal.strdecode.decode_c_str(data, api_name). Success path = bytes.decode() as today. On UnicodeDecodeError, re-raises the same exception type with reason extended to include the originating CUDA API and a bounded hex preview of the buffer.

Implements the helper proposed inline on #2118 ("a tiny helper... source API name plus a bounded repr/hex dump"). #2118 fixed the WSL symptom in cuda_core; this closes the diagnostics gap in cuda_bindings.

Design

• Pure-Python _internal/strdecode.py next to _fast_enum.py — no Cython rebuild
• Same exception type; original chained via from e
• Hex preview, stops at first NUL with stopped at NUL@<offset> marker,
  caps at 64 bytes with +N more

Example

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf8 in position 0:
invalid start byte (returned by nvmlSystemGetProcessName;
bytes=<5 bytes; hex='f8 9a 80 80 af'>)

Scope of this PR

Two files, both hand-written:

• cuda_bindings/cuda/bindings/_internal/strdecode.py — the helper
• cuda_bindings/tests/test_strdecode.py — 11 unit tests

The existing _output_.decode() sites in nvml.error_string,
nvvm.get_error_string, nvfatbin.get_error_string, and
cufile.cufileop_status_error are good candidates to adopt this helper.
Those modules are maintained on the NVIDIA side, so wiring is left to the
maintainers rather than included here.

Refs #2118. Closes #2122.

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[aryanputta]

Requesting review when you have a chance. I kept this PR scoped to the helper itself. If this direction looks good, I can send a follow-up wiring it into the current decode sites in nvml, nvvm, nvfatbin, and cufile.

[rwgk]

Hi @aryanputta, unfortunately we cannot accept external contributions to cuda-bindings :-(

It's not compatible with the cuda-bindings LICENSE terms.

I should probably add that explanation to the automatic bot comment above.