Logging: structured slog messages throughout, and WithLogger options so callers choose the logger

Log messages are lower-case event names with their details as key/value
attributes ("error" for errors), in place of formatted strings.

Loggable package take a WithLogger option as part of their "New*" call,
defaulting to slog.Default(). Each tags its lines with its `component`.

Some debug loggers print directly rather than using slog when in
terminal logging mode.

internal/mock/findatender/generator.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"hash/fnv"
-	"log"
 	"math"
 	"math/rand"
 	"time"
@@ -21,15 +20,18 @@ type Generator struct {
 	cat   *Catalog
 	store *Store
 	rnd   *rand.Rand
+	opts  options
 }
 
 // NewGenerator returns a generator drawing from cat and storing releases in
-// store. The same seed and store contents give the same releases.
-func NewGenerator(cat *Catalog, store *Store, seed int64) *Generator {
+// store. The same seed and store contents give the same releases. It logs to
+// slog.Default() unless given WithLogger.
+func NewGenerator(cat *Catalog, store *Store, seed int64, opts ...Option) *Generator {
 	return &Generator{
 		cat:   cat,
 		store: store,
 		rnd:   rand.New(rand.NewSource(seed)), //nolint:gosec // seeded for repeatable mock data
+		opts:  applyOptions(opts),
 	}
 }
 
@@ -235,9 +237,10 @@ func (g *Generator) CatchUp(
 
 // Run publishes a new release after a random gap between min and max until ctx ends.
 func (g *Generator) Run(ctx context.Context, min, max time.Duration) {
+	logger := g.opts.logger("generator")
 	for {
 		d := g.gap(min, max)
-		log.Printf("generator: next release in %s", d.Round(time.Second))
+		logger.Info("next release", "in", d.Round(time.Second))
 
 		timer := time.NewTimer(d)
 		select {
@@ -249,11 +252,11 @@ func (g *Generator) Run(ctx context.Context, min, max time.Duration) {
 
 		r := g.Make(time.Now())
 		if err := g.store.Append(r); err != nil {
-			log.Printf("generator: storing release: %v", err)
+			logger.Error("storing release failed", "error", err)
 			continue
 		}
 
-		log.Printf("generator: published %s (%s) %s", r.ID, r.Tag[0], r.OCID)
+		logger.Info("published release", "release_id", r.ID, "tag", r.Tag[0], "ocid", r.OCID)
 	}
 }