modularize code, add dummy version of roverd

pi/roverd/brc_dummy.go

@@ -0,0 +1,19 @@
+//go:build dummy
+
+package roverd
+
+import (
+	"context"
+	"log"
+)
+
+type BRCPulser struct{}
+
+func NewBRCPulser(cfg BRCConfig, logger *log.Logger) (*BRCPulser, error) {
+	logger.Printf("[dummy] BRC configured on pin %d", cfg.GPIOPin)
+	return &BRCPulser{}, nil
+}
+
+func (b *BRCPulser) Close() {}
+
+func (b *BRCPulser) Start(ctx context.Context) {}