fix: Rewrite constant_pad_nd to use a single slice layer for performance

[mfeliz-cruise]

Description

Rewrite constant_pad_nd converter to use a single slice layer rather than fill and concat. This is similar to what onnx implements here: https://github.com/onnx/onnx-tensorrt/blob/main/builtin_op_importers.cpp#L3249

Functionality covered by existing tests, shows 5ms perf improvement on internal test.

Fixes # (issue)

Type of change

Please delete options that are not relevant and/or add your own.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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

[narendasan]

LGTM thanks!