draft: Precise spacing

[MojtabaHs]

The original code used padding to simulate spacing, which caused 3 main issues:

1. Unintended padding around the collection.
2. Spacing being twice the intended length. (e.g. passing 4 but seeing 8)
3. The last Item sometimes does not fit into the layout although it there is enough available space.
   You can notice all of these issues in the following example image

Before this PR (With spacing of 4)

---

After this PR (With spacing of 8)

This PR addresses the problem by applying the correct spacing, ensuring that the spacing is separate from the padding:

Additionally, I updated the default spacing from 4 to 8 to better align with the original design intent.

[MojtabaHs]

Here is another example of before and after this PR with some un-even elements:

Before: With spacing of 4

After: With spacing of 8

[gordan-glavas-codecons]

Hey, maybe I'm missing something, but allow for setting the padding around the entire FlowLayout view, i.e the right-hand margin seems to be ignored and always ends up smaller than the left-hand one:

No padding:

Padding (either .padding(), .padding(10), .padding(.horizontal, 10)):

FlowLayout(mode: .vstack,
                   items: items) {
          Text($0)
            .font(.system(size: 12))
            .foregroundColor(.black)
            .padding()
            .background(RoundedRectangle(cornerRadius: 4)
              .border(Color.gray)
              .foregroundColor(Color.gray))
        }.padding()

[MojtabaHs]

Hey, maybe I'm missing something, but allow for setting the padding around the entire FlowLayout view, ...

It seems like the ZStack content does not respect the container size. I will take a look later