Add configuration and CLI foundation

internal/timeutil/clock.go

@@ -0,0 +1,22 @@
+// Package timeutil provides time-zone, clock, and period helpers.
+package timeutil
+
+import "time"
+
+type Clock interface {
+	Now() time.Time
+}
+
+type SystemClock struct{}
+
+func (SystemClock) Now() time.Time {
+	return time.Now()
+}
+
+type FixedClock struct {
+	Time time.Time
+}
+
+func (c FixedClock) Now() time.Time {
+	return c.Time
+}