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.

seesaw/encoder.go

@@ -0,0 +1,49 @@
+package seesaw
+
+import (
+	"errors"
+)
+
+var errInvalidEncoderNumber = errors.New("invalid encoder choice, 0-15 are supported")
+
+// GetEncoderPosition returns the absolute position (or delta since the previous call) of the specified rotary encoder.
+func (d *Device) GetEncoderPosition(encoder uint, asDelta bool) (int32, error) {
+	if encoder >= 16 {
+		return 0, errInvalidEncoderNumber
+	}
+
+	// The function address' upper nibble is the function, the lower nibble selects which encoder to communicate with
+	fnAddr := FunctionAddress(encoder)
+	if asDelta {
+		fnAddr |= FunctionEncoderDelta
+	} else {
+		fnAddr |= FunctionEncoderPosition
+	}
+
+	var buf [4]byte
+	err := d.Read(ModuleEncoderBase, fnAddr, buf[:])
+	if err != nil {
+		return 0, err
+	}
+
+	return int32(buf[0])<<24 | int32(buf[1])<<16 | int32(buf[2])<<8 | int32(buf[3]), nil
+}
+
+// SetEncoderPosition calibrate's the encoder's current absolute position to be whatever the provided position is.
+func (d *Device) SetEncoderPosition(encoder uint, position int32) error {
+	if encoder >= 16 {
+		return errInvalidEncoderNumber
+	}
+
+	// The function address' upper nibble is the function, the lower nibble selects which encoder to communicate with
+	fnAddr := FunctionEncoderPosition | FunctionAddress(encoder)
+
+	buf := [4]byte{
+		byte(position >> 24),
+		byte(position >> 16),
+		byte(position >> 8),
+		byte(position),
+	}
+
+	return d.Write(ModuleEncoderBase, fnAddr, buf[:])
+}