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/fake_test.go

@@ -31,7 +31,6 @@ type fakeAPI struct {
 }
 
 type fakeVol struct {
-	name     string
 	format   string
 	capacity int64
 	backing  string
@@ -94,7 +93,7 @@ func (f *fakeAPI) vol(pool, name string) *fakeVol {
 func (f *fakeAPI) putVol(pool, name, format string, data []byte) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
-	f.pools[pool][name] = &fakeVol{name: name, format: format, capacity: int64(len(data)), data: data}
+	f.pools[pool][name] = &fakeVol{format: format, capacity: int64(len(data)), data: data}
 }
 
 func (f *fakeAPI) volNames(pool string) []string {
@@ -348,7 +347,7 @@ func (f *fakeAPI) StorageVolCreateXML(pool libvirt.StoragePool, raw string, _ li
 	if _, exists := vols[v.Name]; exists {
 		return libvirt.StorageVol{}, lvError(libvirt.ErrStorageVolExist, "storage volume '%s' exists already", v.Name)
 	}
-	fv := &fakeVol{name: v.Name, format: v.Target.Format.Type, capacity: v.Capacity.Value}
+	fv := &fakeVol{format: v.Target.Format.Type, capacity: v.Capacity.Value}
 	if v.BackingStore != nil {
 		fv.backing = v.BackingStore.Path
 	}