scd4x: implement driver for CO2 sensor

Signed-off-by: deadprogram <ron@hybridgroup.com>

scd4x/scd4x_test.go

@@ -0,0 +1,15 @@
+package scd4x
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"tinygo.org/x/drivers/tester"
+)
+
+func TestDefaultI2CAddress(t *testing.T) {
+	c := qt.New(t)
+	bus := tester.NewI2CBus(c)
+	dev := New(bus)
+	c.Assert(dev.Address, qt.Equals, uint8(Address))
+}