Added neg_ method to the PyTorch frontend

[he11owthere]

closes #21915

[github-actions]

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[he11owthere]

@MahmoudAshraf97 Please add "bfloat16" in the with_unsupported_dtypes decorator before running the tests until the issue with ivy.Array.repr method has been fixed as mentioned by Ved in #21447. Thank you! 🙂