mod(element/scrollable): introduce minSize function for Element

The minimal required size can the queried from the containing `Element`
of the `Container` that is provided to the `Scrollable` to dynamically
adjust its size.

Currently abritrary nesting is not supported / tested.

examples/styles/text.zig

@@ -28,7 +28,22 @@ const TextStyles = struct {
     const text = "Example";
 
     pub fn element(this: *@This()) App.Element {
-        return .{ .ptr = this, .vtable = &.{ .content = content } };
+        return .{
+            .ptr = this,
+            .vtable = &.{
+                .minSize = minSize,
+                .content = content,
+            },
+        };
+    }
+
+    fn minSize(ctx: *anyopaque, size: zterm.Point) zterm.Point {
+        _ = ctx;
+        _ = size;
+        return .{
+            .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
+            .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
+        };
     }
 
     fn content(ctx: *anyopaque, _: *const App.Model, cells: []zterm.Cell, size: zterm.Point) !void {
@@ -102,12 +117,6 @@ pub fn main() !void {
 
     var box = try App.Container.init(allocator, .{
         .layout = .{ .direction = .vertical },
-        .size = .{
-            .dim = .{
-                .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
-                .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
-            },
-        },
     }, text_styles.element());
     defer box.deinit();