lakazatong

[Core/Sugar] Allow non-fixed sizing for padding and gap

2

### Overview Extend `.padding` and `.gap` to support explicit sizing rules: `CLAY_SIZING_FIXED`, `CLAY_SIZING_GROW`, or `CLAY_SIZING_PERCENT`. Current API (fixed only): ``` .padding = CLAY_PADDING_ALL(100) ``` Proposed API: ``` .padding = CLAY_PADDING_ALL(CLAY_SIZING_FIXED(100))...