expose fewer internals in packages, for easier software reuse

- prometheus is now behind an interface, they aren't dependencies for the
  reusable components anymore.
- some dependencies have been inverted: instead of packages importing a main
  package to get configuration, the main package now sets configuration in
  these packages. that means fewer internals are pulled in.
- some functions now have new parameters for values that were retrieved from
  package "mox-".

stub/metrics.go

@@ -0,0 +1,43 @@
+package stub
+
+import (
+	"context"
+	"time"
+
+	"golang.org/x/exp/slog"
+)
+
+func HTTPClientObserveIgnore(ctx context.Context, log *slog.Logger, pkg, method string, statusCode int, err error, start time.Time) {
+}
+
+type Counter interface {
+	Inc()
+}
+
+type CounterIgnore struct{}
+
+func (CounterIgnore) Inc() {}
+
+type CounterVec interface {
+	IncLabels(labels ...string)
+}
+
+type CounterVecIgnore struct{}
+
+func (CounterVecIgnore) IncLabels(labels ...string) {}
+
+type Histogram interface {
+	Observe(float64)
+}
+
+type HistogramIgnore struct{}
+
+func (HistogramIgnore) Observe(float64) {}
+
+type HistogramVec interface {
+	ObserveLabels(v float64, labels ...string)
+}
+
+type HistogramVecIgnore struct{}
+
+func (HistogramVecIgnore) ObserveLabels(v float64, labels ...string) {}