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/random_test.go

@@ -0,0 +1,73 @@
+package worldgen
+
+import (
+	"math"
+	"testing"
+)
+
+// Reference vectors captured from the official 26.1.2 server classes
+// (XoroshiroRandomSource / LegacyRandomSource seeded with 42), consumed in
+// order: 5x NextLong, 5x NextIntN(100), then doubles/floats.
+
+func TestXoroshiroVectors(t *testing.T) {
+	x := NewXoroshiro(42)
+
+	wantLong := []int64{
+		-4695948378737616609, 7341713790291473579, -7542733514721318211,
+		4888889476139319686, 8419651034331256779,
+	}
+	for i, w := range wantLong {
+		if got := x.NextLong(); got != w {
+			t.Fatalf("NextLong[%d] = %d, want %d", i, got, w)
+		}
+	}
+
+	wantInt := []int32{28, 93, 40, 73, 75}
+	for i, w := range wantInt {
+		if got := x.NextIntN(100); got != w {
+			t.Fatalf("NextIntN[%d] = %d, want %d", i, got, w)
+		}
+	}
+
+	wantDouble := []float64{0.4990607418038817, 0.4922907789978952, 0.09296765457327383}
+	for i, w := range wantDouble {
+		if got := x.NextDouble(); math.Abs(got-w) > 1e-15 {
+			t.Fatalf("NextDouble[%d] = %v, want %v", i, got, w)
+		}
+	}
+
+	wantFloat := []float32{0.1058414, 0.583224, 0.34108514}
+	for i, w := range wantFloat {
+		if got := x.NextFloat(); math.Abs(float64(got-w)) > 1e-6 {
+			t.Fatalf("NextFloat[%d] = %v, want %v", i, got, w)
+		}
+	}
+}
+
+func TestLegacyVectors(t *testing.T) {
+	r := NewLegacy(42)
+
+	wantLong := []int64{
+		-5025562857975149833, -5843495416241995736, 5694868678511409995,
+		5111195811822994797, -6169532649852302182,
+	}
+	for i, w := range wantLong {
+		if got := r.NextLong(); got != w {
+			t.Fatalf("NextLong[%d] = %d, want %d", i, got, w)
+		}
+	}
+
+	wantInt := []int32{82, 2, 76, 92, 76}
+	for i, w := range wantInt {
+		if got := r.NextIntN(100); got != w {
+			t.Fatalf("NextIntN[%d] = %d, want %d", i, got, w)
+		}
+	}
+
+	wantDouble := []float64{0.6904257605024213, 0.762090173108902, 0.998178600062844}
+	for i, w := range wantDouble {
+		if got := r.NextDouble(); math.Abs(got-w) > 1e-15 {
+			t.Fatalf("NextDouble[%d] = %v, want %v", i, got, w)
+		}
+	}
+}