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.go

@@ -10,10 +10,11 @@ import (
 )
 
 // tracingAPI wraps a libvirtAPI and logs one V(1) line per call after it
-// returns: method, the identifiers it was given, curated results, duration,
-// and the libvirt error fields on failure. At V(2) the same line also
-// carries XML bodies, metadata and address lists. Upload and download
-// bodies are never logged: the seed ISO carries cloud-init.
+// returns: the libvirt API function (rpc=virDomainLookupByName, ...), the
+// identifiers it was given, curated results, duration, and on failure the
+// error with libvirt's code name. At V(2) the same line also carries XML
+// bodies, metadata and address lists. Upload and download bodies are never
+// logged: the seed ISO carries cloud-init.
 type tracingAPI struct {
 	inner libvirtAPI
 	log   logr.Logger
@@ -26,8 +27,11 @@ type tracedCall struct {
 	kv     []any
 }
 
+// begin names the call by its libvirt API function: go-libvirt's method
+// names are the remote procedure names, which are the public vir* API
+// names without the prefix.
 func (t *tracingAPI) begin(method string, kv ...any) *tracedCall {
-	return &tracedCall{t: t, method: method, start: time.Now(), kv: kv}
+	return &tracedCall{t: t, method: "vir" + method, start: time.Now(), kv: kv}
 }
 
 // detail adds key/values that are only worth the bytes at V(2).
@@ -40,7 +44,7 @@ func (c *tracedCall) detail(kv ...any) *tracedCall {
 
 func (c *tracedCall) done(err error, kv ...any) {
 	fields := make([]any, 0, 2+len(c.kv)+len(kv)+10)
-	fields = append(fields, "method", c.method)
+	fields = append(fields, "rpc", c.method)
 	fields = append(fields, c.kv...)
 	fields = append(fields, kv...)
 	fields = append(fields, "duration", time.Since(c.start).Round(time.Microsecond))