`Logic.zeroExtend` should return `this` if `width` is the same as `newWidth`, and `Swizzle` optimization in SV generation

[mkorbel1]

Describe the bug

When zero-extending a signal, if there's nothing to zero-extend, we can just immediately return this rather than go through a Swizzle.

Additionally, when Swizzle gets only one signal with width >0, it shouldn't still add the {} around it.

To Reproduce

• Call zeroExtend on a Logic with the newWidth equal to the width. Note that it creates a swizzle unnecessarily.
• Swizzle two signals, one of which is 0-width, and observe generated SV to contain {} around the one remaining signal.

Expected behavior

No response

Actual behavior

No response

Additional: Dart SDK info

No response

Additional: pubspec.yaml

No response

Additional: Context

No response

[mjayasim9]

Will work on this :)

[mkorbel1]

As part of this, calling swizzle should probably not generate a swizzle module if the number of non-zero-width signals is 1.