feat(container): introduce fixed_size property for fixed sizing of Containers

Moved min_size property from `Container` to the `Scrollable` element,
where it is only used anyway.

src/element.zig

@@ -58,12 +58,16 @@ pub fn Scrollable(Event: type) type {
         /// `Size` of the actual contents where the anchor and the size is
         /// representing the size and location on screen.
         size: Size = .{},
+        /// Minimal `Size` of the scrollable `Container` to be used. If the
+        /// actual scrollable container's size is larger it will be used instead
+        /// (no scrolling will be necessary for that screen size).
+        min_size: Size = .{},
         /// `Size` of the `Container` content that is scrollable and mapped to
         /// the *size* of the `Scrollable` `Element`.
         container_size: Size = .{},
         /// Anchor of the viewport of the scrollable `Container`.
         anchor: Position = .{},
-        /// The actual container, that is scrollable.
+        /// The actual `Container`, that is scrollable.
         container: Container(Event),
 
         pub fn element(this: *@This()) Element(Event) {
@@ -76,8 +80,11 @@ pub fn Scrollable(Event: type) type {
             };
         }
 
-        pub fn init(container: Container(Event)) @This() {
-            return .{ .container = container };
+        pub fn init(container: Container(Event), min_size: Size) @This() {
+            return .{
+                .container = container,
+                .min_size = min_size,
+            };
         }
 
         fn handle(ctx: *anyopaque, event: Event) !void {
@@ -86,7 +93,7 @@ pub fn Scrollable(Event: type) type {
                 .resize => |size| {
                     this.size = size;
                     // TODO: scrollbar space - depending on configuration and only if necessary?
-                    this.container_size = size.max(this.container.minSize());
+                    this.container_size = size.max(this.min_size);
                     this.container_size.anchor = size.anchor;
                     try this.container.handle(.{ .resize = this.container_size });
                 },
@@ -190,7 +197,6 @@ test "scrollable vertical" {
             .direction = .vertical,
             .padding = .all(1),
         },
-        .min_size = .{ .rows = size.rows + 15 },
     }, .{});
     try box.append(try .init(std.testing.allocator, .{
         .rectangle = .{ .fill = .grey },
@@ -200,7 +206,7 @@ test "scrollable vertical" {
     }, .{}));
     defer box.deinit();
 
-    var scrollable: Scrollable(event.SystemEvent) = .init(box);
+    var scrollable: Scrollable(event.SystemEvent) = .init(box, .{ .rows = size.rows + 15 });
 
     var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
         .border = .{
@@ -265,7 +271,6 @@ test "scrollable horizontal" {
             .direction = .horizontal,
             .padding = .all(1),
         },
-        .min_size = .{ .cols = size.cols + 15 },
     }, .{});
     try box.append(try .init(std.testing.allocator, .{
         .rectangle = .{ .fill = .grey },
@@ -275,7 +280,7 @@ test "scrollable horizontal" {
     }, .{}));
     defer box.deinit();
 
-    var scrollable: Scrollable(event.SystemEvent) = .init(box);
+    var scrollable: Scrollable(event.SystemEvent) = .init(box, .{ .cols = size.cols + 15 });
 
     var container: Container(event.SystemEvent) = try .init(std.testing.allocator, .{
         .border = .{