Make the libvirt trace compact: libvirt API names, one error field, terse test output

The first live run showed the trace working but noisy: testr printed
ts/level/msg and the per-run constants on every line, the error text
appeared twice, host appeared twice on image-cache lines, and the Go
method name was less useful than the libvirt function it maps to.

The tracer now logs rpc=virDomainLookupByName (go-libvirt's names are the
public API names without the vir prefix), error plus libvirtError (code
name) and libvirtCode, and image.go stops re-adding host. The integration
test replaces testr with a compact logr sink: time, logger name, the rpc
as headline, then fields, with provider/host/name omitted since the first
line of the run states them. Docs and execution log updated.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/provider/kvm/image.go

@@ -101,7 +101,7 @@ func (c *imageCache) ensure(ctx context.Context, log logr.Logger, api libvirtAPI
 		return "", err
 	}
 	if ready {
-		log.V(1).Info("base image already cached", "host", hostName, "volume", src.volumeName())
+		log.V(1).Info("base image already cached", "volume", src.volumeName())
 		return api.StorageVolGetPath(base)
 	}
 	if err := deleteIfExists(api, pool, src.markerName()); err != nil {
@@ -170,7 +170,7 @@ func (c *imageCache) fetch(ctx context.Context, log logr.Logger, api libvirtAPI,
 	}
 
 	log.Info("fetching base image into host pool",
-		"host", hostName, "pool", pool.Name, "volume", src.volumeName(),
+		"pool", pool.Name, "volume", src.volumeName(),
 		"url", src.URL, "bytes", resp.ContentLength)
 	start := time.Now()
 
@@ -212,7 +212,7 @@ func (c *imageCache) fetch(ctx context.Context, log logr.Logger, api libvirtAPI,
 		return libvirt.StorageVol{}, fmt.Errorf("writing image marker: %w", err)
 	}
 	log.Info("base image cached",
-		"host", hostName, "volume", src.volumeName(), "sha256", digest,
+		"volume", src.volumeName(), "sha256", digest,
 		"bytes", resp.ContentLength, "duration", time.Since(start).Round(time.Second))
 	return base, nil
 }