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/kvm_test.go

@@ -925,15 +925,15 @@ func TestLogging_verbosityTiers(t *testing.T) {
 			wantLines: []string{
 				`kvm/libvirt "level"=1 "msg"="libvirt host connected"`,
 				`"msg"="libvirt call"`,
-				`"method"="DomainLookupByName"`,
-				`"libvirtCodeName"="ErrNoDomain"`,
-				`"method"="StorageVolUpload"`,
-				`"method"="DomainDefineXML"`,
-				`"method"="DomainCreate"`,
-				`"method"="DomainInterfaceAddresses"`,
-				`"method"="ConnectListAllDomains"`,
-				`"method"="DomainUndefineFlags"`,
-				`"method"="StorageVolDelete"`,
+				`"rpc"="virDomainLookupByName"`,
+				`"libvirtError"="ErrNoDomain"`,
+				`"rpc"="virStorageVolUpload"`,
+				`"rpc"="virDomainDefineXML"`,
+				`"rpc"="virDomainCreate"`,
+				`"rpc"="virDomainInterfaceAddresses"`,
+				`"rpc"="virConnectListAllDomains"`,
+				`"rpc"="virDomainUndefineFlags"`,
+				`"rpc"="virStorageVolDelete"`,
 				`"provider"="kvm-home"`,
 				`"host"="nas1"`,
 				`"name"="` + testName + `"`,