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/config/print.go

@@ -1,10 +1,13 @@
 package config
 
 import (
+	"context"
 	"fmt"
 	"log/slog"
 	"maps"
 	"slices"
+
+	"git.avsdev.uk/Go/job-search/internal/logging"
 )
 
 // PrintTerminal prints the configuration to stdout as String formats it.
@@ -23,31 +26,33 @@ func (conf JobSearchConfig) PrintYaml() {
 }
 
 // PrintLog logs each configuration key and value, sorted by key, at atLevel:
-// debug, warn, error, or info for any other level.
+// debug, warn, error, or info for any other level. On a terminal it logs one
+// line and prints the values under it as "key = value" lines; elsewhere each
+// value is a log entry of its own.
 func (conf JobSearchConfig) PrintLog(atLevel slog.Level) {
-	var logFn func(args ...interface{})
-
 	switch atLevel {
-	case slog.LevelDebug:
-		logFn = func(args ...interface{}) {
-			slog.Debug(fmt.Sprint(args...))
-		}
-	case slog.LevelError:
-		logFn = func(args ...interface{}) {
-			slog.Error(fmt.Sprint(args...))
-		}
-	case slog.LevelWarn:
-		logFn = func(args ...interface{}) {
-			slog.Warn(fmt.Sprint(args...))
-		}
+	case slog.LevelDebug, slog.LevelWarn, slog.LevelError:
 	default:
-		logFn = func(args ...interface{}) {
-			slog.Info(fmt.Sprint(args...))
-		}
+		atLevel = slog.LevelInfo
 	}
 
+	ctx := context.Background()
+	logger := slog.Default()
 	flat := conf.Flatten()
-	for _, k := range slices.Sorted(maps.Keys(flat)) {
-		logFn("\t", k, " = ", flat[k])
+	keys := slices.Sorted(maps.Keys(flat))
+
+	if logging.WritesToTerminal(logger.Handler()) {
+		if !logger.Enabled(ctx, atLevel) {
+			return
+		}
+		logger.Log(ctx, atLevel, "config values", "count", len(keys))
+		for _, key := range keys {
+			logging.PrintToTerminal(fmt.Sprintf("\t%s = %v", key, flat[key]))
+		}
+		return
+	}
+
+	for _, key := range keys {
+		logger.Log(ctx, atLevel, "config value", "key", key, "value", flat[key])
 	}
 }