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 CBOR field names, so tokens made before still decode. 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/signature/quality_fit_test.go

@@ -5,22 +5,26 @@ import (
 	"testing"
 	"time"
 
+	"sneak.berlin/go/pixa/internal/imagerequest"
 	"sneak.berlin/go/pixa/internal/signature"
 )
 
 // signedQualityFitRequest returns a request signed for quality 85 and fit
 // mode "cover", the effective defaults the handler applies before
 // verification.
-func signedQualityFitRequest(signer *signature.Signer) *signature.Request {
-	req := &signature.Request{
-		SourceHost: testHost,
-		SourcePath: testPath,
-		Width:      800,
-		Height:     600,
-		Format:     testFormatWebP,
-		Quality:    85,
-		FitMode:    testFitCover,
-		Expires:    time.Now().Add(1 * time.Hour),
+func signedQualityFitRequest(signer *signature.Signer) *imagerequest.Request {
+	req := &imagerequest.Request{
+		Source: imagerequest.Source{
+			Host: testHost,
+			Path: testPath,
+		},
+		Transform: imagerequest.Transform{
+			Size:    imagerequest.Size{Width: 800, Height: 600},
+			Format:  testFormatWebP,
+			Quality: 85,
+			FitMode: testFitCover,
+		},
+		Expires: time.Now().Add(1 * time.Hour),
 	}
 	req.Signature = signer.Sign(req)
 
@@ -40,15 +44,15 @@ func TestSigner_Verify_QualityAndFitAreSigned(t *testing.T) {
 
 	cases := []struct {
 		name   string
-		tamper func(r *signature.Request)
+		tamper func(r *imagerequest.Request)
 	}{
 		{
 			name:   "replayed with different quality",
-			tamper: func(r *signature.Request) { r.Quality = 40 },
+			tamper: func(r *imagerequest.Request) { r.Transform.Quality = 40 },
 		},
 		{
 			name:   "replayed with different fit mode",
-			tamper: func(r *signature.Request) { r.FitMode = testFitContain },
+			tamper: func(r *imagerequest.Request) { r.Transform.FitMode = testFitContain },
 		},
 	}