add: Direct Renderer implementation rendering the fixed size of the root Container

A corresponding example has been added, which is very minimalistic as of now,
but will add further functionality to test the corresponding workflow that is
usual in `zterm` such that it in the best case only a swap in the renderer to
switch from alternate mode drawing to direct drawing.

build.zig

@@ -24,6 +24,8 @@ pub fn build(b: *std.Build) void {
         palette,
         // error handling
         errors,
+        // non alternate screen applications
+        direct,
     };
 
     const example = b.option(Examples, "example", "Example to build and/or run. (default: all)") orelse .all;
@@ -73,6 +75,8 @@ pub fn build(b: *std.Build) void {
                     .palette => "examples/styles/palette.zig",
                     // error handling
                     .errors => "examples/errors.zig",
+                    // non-alternate screen
+                    .direct => "examples/direct.zig",
                     .all => unreachable, // should never happen
                 }),
                 .target = target,