Proper type unification & promotions (scalars + vectors)

[yuvimittal]

Summary

Centralize numeric unification: int widths (sext/zext), signedness, FP ranks (half/float/double/fp128), and scalar↔vector (splat with cast). Use this everywhere (binops, compares, FMA).

Additional Information

Code of Conduct

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[omsherikar]

@yuvimittal Can I work on this issue?

[yuvimittal]

@omsherikar yes sure! I will assign it to you

[omsherikar]

@omsherikar yes sure! I will assign it to you

Thanks! @yuvimittal I have raised the PR mentioning this issue already, can you please review it?