Define the default max_concurrent_processing in internal/config

The default is configuration, so it now sits with the other defaults as
config.DefaultMaxConcurrentProcessing, and imageprocessor.New reads it
from there for a value below 1. internal/config no longer imports
internal/imageprocessor, so the packages that import internal/config do
not build against libvips.

Model: opus-5-5

internal/imageprocessor/imageprocessor.go

@@ -7,11 +7,11 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"runtime"
 	"sync"
 	"time"
 
 	"github.com/davidbyttow/govips/v2/vips"
+	"sneak.berlin/go/pixa/internal/config"
 )
 
 // vipsOnce ensures vips is initialized exactly once.
@@ -179,19 +179,10 @@ type Params struct {
 	// If <= 0, DefaultMaxInputBytes is used.
 	MaxInputBytes int64
 	// MaxConcurrentProcessing is the most images processed at once.
-	// If <= 0, DefaultMaxConcurrentProcessing() is used.
+	// If <= 0, config.DefaultMaxConcurrentProcessing() is used.
 	MaxConcurrentProcessing int
 }
 
-// DefaultMaxConcurrentProcessing returns the most images processed at once
-// when none is set: half the CPUs Go uses (runtime.GOMAXPROCS(0), which
-// follows a container's CPU limit), rounded down, and at least 1.
-func DefaultMaxConcurrentProcessing() int {
-	const cpusPerImage = 2
-
-	return max(runtime.GOMAXPROCS(0)/cpusPerImage, 1)
-}
-
 // New creates a new image processor with the given parameters.
 // A zero-value Params{} uses sensible defaults.
 func New(params Params) *ImageProcessor {
@@ -204,7 +195,7 @@ func New(params Params) *ImageProcessor {
 
 	maxConcurrentProcessing := params.MaxConcurrentProcessing
 	if maxConcurrentProcessing <= 0 {
-		maxConcurrentProcessing = DefaultMaxConcurrentProcessing()
+		maxConcurrentProcessing = config.DefaultMaxConcurrentProcessing()
 	}
 
 	return &ImageProcessor{