Add graphics levels, screen choices and the rest of the simulator's keys

Six levels of detail climbing in even steps, High being where a player with no
settings of their own starts. Five parts of the picture can also take a level
of their own. Resolutions start from the monitors in the computer.

uartfeature with nothing selected writes "no no no no"; uart and uarttune are
written whole or not at all. On Linux the file's contents tell a Windows build,
a native one and a script from a note that merely has the execute bit.

StarterNG.Tests/StepsTests.cs

@@ -0,0 +1,42 @@
+using StarterNG.Domain.Settings;
+
+namespace StarterNG.Tests;
+
+public class StepsTests
+{
+    [Fact]
+    public void A_value_among_the_steps_leaves_them_as_they_are()
+    {
+        Assert.Same(Steps.FrameRateLimits, Steps.With(Steps.FrameRateLimits, 144));
+    }
+
+    [Fact]
+    public void A_value_between_the_steps_joins_them_in_order()
+    {
+        var steps = Steps.With(Steps.FrameRateLimits, 58);
+
+        Assert.Equal(Steps.FrameRateLimits.Length + 1, steps.Count);
+        Assert.Equal(new double[] { 50, 58, 60 }, steps.Skip(Steps.IndexOf(steps, 50)).Take(3));
+    }
+
+    [Fact]
+    public void Values_past_either_end_join_at_that_end()
+    {
+        Assert.Equal(0.5, Steps.With(Steps.Anisotropy, 0.5)[0]);
+        Assert.Equal(500, Steps.With(Steps.FrameRateLimits, 500)[^1]);
+    }
+
+    [Fact]
+    public void The_frame_rate_limits_start_with_none()
+    {
+        Assert.Equal(new double[] { 0, 10, 20 }, Steps.With(Steps.FrameRateLimits, 10).Take(3));
+    }
+
+    [Fact]
+    public void A_step_is_found_from_its_rounding_in_the_file()
+    {
+        // 1/300 is written as 0.003333.
+        Assert.Equal(0, Steps.IndexOf(Steps.ReflectionUpdates, 0.003333));
+        Assert.Equal(-1, Steps.IndexOf(Steps.ReflectionUpdates, 0.0033));
+    }
+}