Declare only the tables and columns pixa writes and reads (closes #310)

Removes output_content and request_cache, which nothing writes, and every
column that was written but never read: the host, path, query, content_type
and fetched_at of source_content, the content_type and created_at of
variant_content, and the status_code, error_message and fetched_at of
negative_cache.

StoreSource no longer takes the fetch result and LookupSource returns only
the source key. StoreVariant no longer takes a content type and
StoreNegative no longer takes a status code or message, so
extractStatusCode and the status constants, which only fed status_code,
are gone. Reconciliation adopts a variant file without opening it, as its
row no longer records a content type. Tests that set or checked a removed
column follow.

Model: opus-5-5

internal/imgcache/source_content_internal_test.go

@@ -7,7 +7,6 @@ import (
 	"path/filepath"
 	"testing"
 
-	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
@@ -32,10 +31,8 @@ func TestStoreSource_StoresIdenticalBytesOfTwoURLsTwice(t *testing.T) {
 	}
 
 	for sourcePath, key := range keys {
-		rows := countRows(t, cache, `
-			SELECT COUNT(*) FROM source_content
-			WHERE source_key = ? AND source_host = ? AND source_path = ?
-		`, string(key), testHostCDN, sourcePath)
+		rows := countRows(t, cache,
+			`SELECT COUNT(*) FROM source_content WHERE source_key = ?`, string(key))
 		if rows != 1 {
 			t.Errorf("%s has %d source_content rows, want 1", sourcePath, rows)
 		}
@@ -87,10 +84,10 @@ func TestEvictSourceBlob_LeavesSourceWithIdenticalBytesServed(t *testing.T) {
 		t.Errorf("the evicted source still has %d source_content rows", n)
 	}
 
-	kept, contentType, err := cache.LookupSource(t.Context(), &imagerequest.Request{
+	kept, err := cache.LookupSource(t.Context(), &imagerequest.Request{
 		Source: imagerequest.Source{Host: testHostCDN, Path: "/kept.jpg"},
 	})
-	t.Logf("LookupSource() of the kept source = %q, %q, error %v", kept, contentType, err)
+	t.Logf("LookupSource() of the kept source = %q, error %v", kept, err)
 
 	if err != nil || kept == "" {
 		t.Fatalf("LookupSource() of the kept source = %q, %v; want it cached", kept, err)
@@ -130,10 +127,8 @@ func TestStoreSource_FailedRowWriteLeavesNoFile(t *testing.T) {
 	req := &imagerequest.Request{
 		Source: imagerequest.Source{Host: testHostCDN, Path: testPathCat},
 	}
-	result := &httpfetcher.FetchResult{ContentType: testContentTypeJPEG}
-
 	key, err := cache.StoreSource(t.Context(), req,
-		bytes.NewReader([]byte("source bytes")), result)
+		bytes.NewReader([]byte("source bytes")))
 	t.Logf("StoreSource() = %q, error = %v", key, err)
 
 	if err == nil {