Initial commit: RegionIO Minecraft server core (26.1.2/protocol 775)

Vanilla-faithful overworld generator (final_density + multi-noise biomes),
full connection lifecycle (status/login/configuration/play), chunk streaming,
creative block editing, and the protocol/nbt/registry infrastructure.

internal/worldgen/improved_noise_test.go

@@ -0,0 +1,32 @@
+package worldgen
+
+import (
+	"math"
+	"testing"
+)
+
+func TestImprovedNoiseVectors(t *testing.T) {
+	n := NewImprovedNoise(NewXoroshiro(42))
+
+	for _, c := range []struct {
+		name     string
+		got, want float64
+	}{
+		{"xo", n.Xo, 190.83062484342904},
+		{"yo", n.Yo, 101.88674612737026},
+		{"zo", n.Zo, 151.323544791807},
+	} {
+		if math.Abs(c.got-c.want) > 1e-9 {
+			t.Fatalf("%s = %v, want %v", c.name, c.got, c.want)
+		}
+	}
+
+	pts := [][3]float64{{0.5, 0.5, 0.5}, {1.5, 2.5, 3.5}, {100.1, 64.0, -200.7}, {-12.3, 5.0, 7.7}}
+	want := []float64{0.078420838879807, 0.42903440359153633, 0.041997176611984766, -0.07019565638436798}
+	for i, p := range pts {
+		got := n.Noise(p[0], p[1], p[2])
+		if math.Abs(got-want[i]) > 1e-12 {
+			t.Fatalf("Noise%v = %v, want %v", p, got, want[i])
+		}
+	}
+}