Pad MXFP8 scale inverses at the time of creation

[ksivaman]

Description

Scaling factors need to be a multiple of 128 and 4 in the m, k directions respectively. This PR creates the correct sized scale inverses instead of padding them later.

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• 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)
• Infra/Build change
• Code refactoring

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[timmoon10]

Looks good, my changes are stylistic.

Once we have this in, we can modify the MXFP8 tests to have the same tensor dims as FP8 (#1435). This will be useful for maintaining tight numerical tolerances and fixing some remaining test failures.