Add attention mask skip tests, tokenizer padding edge case tests, and…
Author: MosadCreates
Pull request: yes
Labels: name: Code agent slop

… benchmark harness

- Comprehensive unit tests for _ignore_causal_mask_sdpa and _ignore_bidirectional_mask_sdpa, covering padding, tracing, local attention, and edge cases (14 tests, all passing).
- Tokenizer padding edge case tests for GPT-2 and LLaMA covering left/right padding, pad_token=eos_token conflicts, and variable-length batched generation.
- Benchmark harness to measure throughput impact of causal mask skip logic at varying batch sizes and sequence lengths.

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Thank you for your contribution 🤗!

## CI Security Gate — automatic approval blocked

This PR was **not** automatically approved for CI because the security gate failed.

**Possible reasons:**
- The PR touches 50 or more files — only PRs with fewer than 50 changed files are automatically approved
- A changed file is outside the allowed directories (`src/`, `tests/`, `docs/`, `utils/`), has a disallowed extension (only `.py`, `.txt`, `.md` permitted outside `tests/` and `docs/`), or is not `.md`/`.yml` inside `docs/`
- A new high-severity security issue was detected in the changed Python files (Bandit check)

See the [workflow run](https://github.com/huggingface/transformers/actions/runs/28291116631) for the exact violations.

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**CI Dashboard:** [View test results in Grafana](https://transformers-ci.lor-e.huggingface.cool/d/pytest-observability-by-pr/pytest-observability-branch?var-pr=46934)