add(error): introduce zterm.Error containing all zterm errors with their corresponding description

src/container.zig

@@ -6,6 +6,7 @@ const Cell = @import("cell.zig");
 const Color = @import("color.zig").Color;
 const Size = @import("size.zig").Size;
 const Style = @import("style.zig");
+const Error = @import("error.zig").Error;
 
 const log = std.log.scoped(.container);
 
@@ -144,7 +145,7 @@ pub const Rectangle = packed struct {
     /// children accordingly without removing the coloring of the `Rectangle`
     fill: Color = .default,
 
-    // NOTE: caller owns `cells` slice and ensures that `cells.len == size.cols * size.rows`
+    // NOTE: caller owns `Cells` slice and ensures that `cells.len == size.cols * size.rows`
     pub fn contents(this: @This(), cells: []Cell, size: Size) void {
         std.debug.assert(cells.len == @as(usize, size.cols) * @as(usize, size.rows));
 
@@ -600,8 +601,8 @@ pub fn Container(comptime Event: type) type {
                         size.rows,
                     });
                     this.size = size;
-                    if (this.properties.fixed_size.cols > 0 and size.cols < this.properties.fixed_size.cols) return error.TooSmall;
-                    if (this.properties.fixed_size.rows > 0 and size.rows < this.properties.fixed_size.rows) return error.TooSmall;
+                    if (this.properties.fixed_size.cols > 0 and size.cols < this.properties.fixed_size.cols) return Error.TooSmall;
+                    if (this.properties.fixed_size.rows > 0 and size.rows < this.properties.fixed_size.rows) return Error.TooSmall;
 
                     try this.element.handle(event);
 
@@ -623,8 +624,8 @@ pub fn Container(comptime Event: type) type {
                     }
                     // check if the available screen is large enough
                     switch (layout.direction) {
-                        .horizontal => if (fixed_size.cols > size.cols) return error.TooSmall,
-                        .vertical => if (fixed_size.rows > size.rows) return error.TooSmall,
+                        .horizontal => if (fixed_size.cols > size.cols) return Error.TooSmall,
+                        .vertical => if (fixed_size.rows > size.rows) return Error.TooSmall,
                     }
                     const sides = this.properties.border.sides;
                     const padding = layout.padding;

src/error.zig

@@ -0,0 +1,4 @@
+pub const Error = error{
+    /// Thrown when a `Container` is too small to be rendered in the current screen part.
+    TooSmall,
+};

src/zterm.zig

@@ -8,6 +8,7 @@ pub const input = @import("input.zig");
 pub const testing = @import("testing.zig");
 
 pub const App = @import("app.zig").App;
+pub const Error = @import("error.zig").Error;
 // App also exports further types once initialized with the user events at compile time:
 // `App.Container`
 // `App.Element`
@@ -31,6 +32,7 @@ test {
     _ = @import("terminal.zig");
     _ = @import("container.zig");
     _ = @import("queue.zig");
+    _ = @import("error.zig");
 
     _ = color;
     _ = size;