feat: add support for seesaw encoders

Adds the necessary function addresses for reading and writing encoders on a seesaw.
Also provides two helper functions to make this easier.

examples/seesaw/rotary-encoder/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/seesaw"
+)
+
+// example reading the position of a rotary encoder (4991) powered by a seesaw
+// https://learn.adafruit.com/adafruit-i2c-qt-rotary-encoder/arduino
+func main() {
+	// This assumes you are using an Adafruit QT Py RP2040 for its Stemma QT connector
+	// https://www.adafruit.com/product/4900
+	i2c := machine.I2C1
+	i2c.Configure(machine.I2CConfig{
+		SCL: machine.I2C1_QT_SCL_PIN,
+		SDA: machine.I2C1_QT_SDA_PIN,
+	})
+
+	dev := seesaw.New(i2c)
+	dev.Address = 0x36
+
+	for {
+		time.Sleep(time.Second)
+
+		pos, err := dev.GetEncoderPosition(0, false)
+		if err != nil {
+			println(err)
+			continue
+		}
+
+		println(pos)
+	}
+}