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/imgcache/eviction.go

@@ -11,6 +11,8 @@ import (
 	"path/filepath"
 	"strings"
 	"time"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
 // DefaultEvictionInterval is how often the background evictor checks
@@ -85,7 +87,7 @@ func (c *Cache) UsageBytes(ctx context.Context) (int64, error) {
 // source content blob (identified by contentHash).
 type evictionCandidate struct {
 	isVariant      bool
-	cacheKey       VariantKey
+	cacheKey       imagerequest.VariantKey
 	contentHash    ContentHash
 	sizeBytes      int64
 	lastAccessedAt string
@@ -240,7 +242,7 @@ func (c *Cache) variantCandidates(ctx context.Context) ([]evictionCandidate, err
 			return nil, fmt.Errorf("failed to scan variant candidate: %w", err)
 		}
 
-		candidate.cacheKey = VariantKey(key)
+		candidate.cacheKey = imagerequest.VariantKey(key)
 		candidates = append(candidates, candidate)
 	}
 
@@ -300,7 +302,9 @@ func (c *Cache) sourceCandidates(ctx context.Context) ([]evictionCandidate, erro
 // file. The metaCache entry goes before the files; a GetVariant that
 // read them just before may put it back, and the next GetVariant then
 // fails to open the file and removes it again.
-func (c *Cache) evictVariant(ctx context.Context, cacheKey VariantKey) error {
+func (c *Cache) evictVariant(
+	ctx context.Context, cacheKey imagerequest.VariantKey,
+) error {
 	_, err := c.db.ExecContext(ctx,
 		`DELETE FROM variant_content WHERE cache_key = ?`, string(cacheKey))
 	if err != nil {
@@ -648,7 +652,7 @@ func (c *Cache) reconcileVariantFiles(ctx context.Context) error {
 				return nil
 			}
 
-			return c.reconcileVariantFile(ctx, path, entry, VariantKey(name))
+			return c.reconcileVariantFile(ctx, path, entry, imagerequest.VariantKey(name))
 		},
 	)
 }
@@ -659,7 +663,7 @@ func (c *Cache) reconcileVariantFiles(ctx context.Context) error {
 // crash or a restored snapshot can leave it, is removed with its row and
 // a warning naming it, so the variant is converted again.
 func (c *Cache) reconcileVariantFile(
-	ctx context.Context, path string, entry fs.DirEntry, cacheKey VariantKey,
+	ctx context.Context, path string, entry fs.DirEntry, cacheKey imagerequest.VariantKey,
 ) error {
 	info, err := entry.Info()
 	if err != nil {
@@ -691,7 +695,7 @@ func (c *Cache) reconcileVariantFile(
 // adoptVariantFile inserts an accounting row for a variant file that
 // has none, using the file's size and modification time.
 func (c *Cache) adoptVariantFile(
-	ctx context.Context, path string, info fs.FileInfo, cacheKey VariantKey,
+	ctx context.Context, path string, info fs.FileInfo, cacheKey imagerequest.VariantKey,
 ) error {
 	modTime := info.ModTime().UTC().Format(sqliteTimestampLayout)
 	contentType := c.variantContentTypeFromSidecar(path)
@@ -731,7 +735,7 @@ func (c *Cache) variantContentTypeFromSidecar(variantPath string) string {
 // reconcileVariantRows drops accounting rows whose variant files are
 // missing, so the database never references deleted content.
 func (c *Cache) reconcileVariantRows(ctx context.Context) error {
-	var after VariantKey
+	var after imagerequest.VariantKey
 
 	for {
 		keys, err := c.variantKeysAfter(ctx, after)
@@ -772,9 +776,9 @@ func (c *Cache) reconcileVariantRows(ctx context.Context) error {
 // variantKeysAfter returns, in order, up to c.reconciliationPageSize
 // tracked variant cache keys that sort after the given one.
 func (c *Cache) variantKeysAfter(
-	ctx context.Context, after VariantKey,
-) ([]VariantKey, error) {
-	return queryStringColumn[VariantKey](ctx, c.db, `
+	ctx context.Context, after imagerequest.VariantKey,
+) ([]imagerequest.VariantKey, error) {
+	return queryStringColumn[imagerequest.VariantKey](ctx, c.db, `
 		SELECT cache_key FROM variant_content
 		WHERE cache_key > ? ORDER BY cache_key LIMIT ?
 	`, "variant keys", "variant key", string(after), c.reconciliationPageSize)