One image request type instead of five (closes #307)

The new package internal/imagerequest holds the request type, its two
parts Source and Transform, the Format and Fit types, the dimension and
fit checks, the /v1/image/ path parsing and the variant key; it imports
no other package of pixa. imgcache.ParsedURL, imgcache.ImageRequest,
signature.Request, imageprocessor.Request, the second Size, format and
fit types and the conversions between them are gone. The image
processor takes a Transform only. encurl keeps a private struct with the
token's short CBOR field names. VariantKey moves with the function that
makes it. Tests follow the moved and renamed code; the tests of the
removed conversions go with them.

Model: opus-5-5

internal/handlers/image_errors_internal_test.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
+	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/imgcache"
 	"sneak.berlin/go/pixa/internal/signature"
 )
@@ -84,15 +85,18 @@ func photoURLWithSig(host, sig string, expires time.Time) string {
 // photoSignature returns the signature of photoURL(host) at the default
 // quality and fit, made with key and expiring at expires.
 func photoSignature(key, host string, expires time.Time) string {
-	return signature.New(key).Sign(&signature.Request{
-		SourceHost: host,
-		SourcePath: photoPath,
-		Width:      50,
-		Height:     50,
-		Format:     string(imgcache.FormatJPEG),
-		Quality:    85,
-		FitMode:    string(imgcache.FitCover),
-		Expires:    expires,
+	return signature.New(key).Sign(&imagerequest.Request{
+		Source: imagerequest.Source{
+			Host: host,
+			Path: photoPath,
+		},
+		Transform: imagerequest.Transform{
+			Size:    imagerequest.Size{Width: 50, Height: 50},
+			Format:  imagerequest.FormatJPEG,
+			Quality: 85,
+			FitMode: imagerequest.FitCover,
+		},
+		Expires: expires,
 	})
 }
 
@@ -353,15 +357,18 @@ func TestHandleImage_HashInSourcePathOrQuery_Returns400(t *testing.T) {
 	photos := newPhotoFetcher(t, allowlistedHost, signedHost)
 	exp := time.Now().Add(time.Hour)
 
-	sig := signature.New(testSigningKey).Sign(&signature.Request{
-		SourceHost: signedHost,
-		SourcePath: photoPath + "#x",
-		Width:      50,
-		Height:     50,
-		Format:     string(imgcache.FormatJPEG),
-		Quality:    85,
-		FitMode:    string(imgcache.FitCover),
-		Expires:    exp,
+	sig := signature.New(testSigningKey).Sign(&imagerequest.Request{
+		Source: imagerequest.Source{
+			Host: signedHost,
+			Path: photoPath + "#x",
+		},
+		Transform: imagerequest.Transform{
+			Size:    imagerequest.Size{Width: 50, Height: 50},
+			Format:  imagerequest.FormatJPEG,
+			Quality: 85,
+			FitMode: imagerequest.FitCover,
+		},
+		Expires: exp,
 	})
 
 	tests := []struct {