Simplify the KVM provider after the /simplify review

Collapse duplicated logic the review found in PR #5 without changing
behaviour: one releaseFinalizer helper for the four finalizer exits in
reconcileDelete, classify reusing isClassified and provider.Class, the
image URL check and format/firmware values shared from the provider
package, imageSource and the metadata parser embedding their config
structs instead of copying fields, and the SSH loader as a small struct
that keeps only the SSH fields and is seeded by New instead of loading
the key twice. Tracing builds its V(2)-only lists only at V(2).

Tests: drop a duplicate New test, fold near-identical tests into tables
(connection drops, metadata parsing, cached images), add mustSSHAuth,
and use wantClass where classes were checked by hand.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/provider/kvm/image.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"net/url"
 	"strings"
 	"sync"
 	"time"
@@ -22,11 +21,8 @@ import (
 // imageSource is a resolved placement.image: either an entry from the
 // provider's images map (Key set) or a URL given directly.
 type imageSource struct {
-	Key      string
-	URL      string
-	SHA256   string
-	Format   string
-	Firmware string
+	Key string
+	provider.KVMImage
 }
 
 // resolveImage maps placement.image to a source. Anything that is neither a
@@ -34,11 +30,10 @@ type imageSource struct {
 // surface, not retry.
 func resolveImage(cfg provider.KVMConfig, image string) (imageSource, error) {
 	if img, ok := cfg.Images[image]; ok {
-		return imageSource{Key: image, URL: img.URL, SHA256: img.SHA256, Format: img.Format, Firmware: img.Firmware}, nil
+		return imageSource{Key: image, KVMImage: img}, nil
 	}
-	u, err := url.Parse(image)
-	if err == nil && (u.Scheme == "http" || u.Scheme == "https") && u.Host != "" {
-		return imageSource{URL: image, Format: formatQcow2, Firmware: firmwareUEFI}, nil
+	if provider.IsHTTPURL(image) {
+		return imageSource{KVMImage: imageDefaults(provider.KVMImage{URL: image})}, nil
 	}
 	return imageSource{}, fmt.Errorf("%w: placement.image %q is neither a key in kvm.images nor an http(s) URL",
 		provider.ErrPermanent, image)