fix: optimize attention decomposition

[fs-eire]

Description

Align attention decomposition behavior with the ONNX graph.

This PR does the following:

• Restrict attention-mask Select choices to scalars while preserving mask polarity and -inf semantics.
• Preserve static arange operations as TensorRT LINSPACE Fill layers.
• Add regression coverage for attention masks and static arange conversion.

With this change, Torch-TensorRT is able to generate optimized engine with a pattern that an attention using a causal mask AND a padding mask, when decompose_attention=True.

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project (You can use the linters)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes
• I have added the relevant labels to my PR in so that relevant reviewers are notified