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/trace_test.go

@@ -119,7 +119,7 @@ func TestTracingAPI_logsEveryMethod(t *testing.T) {
 			if len(lines) != 1 {
 				t.Fatalf("logged %d lines, want exactly 1:\n%s", len(lines), strings.Join(lines, "\n"))
 			}
-			for _, want := range []string{`"msg"="libvirt call"`, `"method"="` + tc.method + `"`, `"duration"=`} {
+			for _, want := range []string{`"msg"="libvirt call"`, `"rpc"="vir` + tc.method + `"`, `"duration"=`} {
 				if !strings.Contains(lines[0], want) {
 					t.Errorf("line missing %s:\n%s", want, lines[0])
 				}
@@ -176,13 +176,13 @@ func TestTracingAPI_errorFields(t *testing.T) {
 		{
 			name:   "libvirt error carries code, name and message",
 			inject: lvError(libvirt.ErrNoDomain, "Domain not found: no domain with matching name"),
-			want:   []string{`"error"=`, `"libvirtCode"=42`, `"libvirtCodeName"="ErrNoDomain"`, `"libvirtMessage"="Domain not found`},
+			want:   []string{`"error"="Domain not found`, `"libvirtError"="ErrNoDomain"`, `"libvirtCode"=42`},
 		},
 		{
 			name:    "transport error has no libvirt fields",
 			inject:  io.EOF,
 			want:    []string{`"error"="EOF"`},
-			notWant: []string{`"libvirtCode"`},
+			notWant: []string{`"libvirtError"`, `"libvirtCode"`},
 		},
 	}
 	for _, tc := range tests {