proxmox: config block, IDs, marks, state mapping, classify, registration

Phase 2 of the proxmox provider plan. Adds the proxmox: config block with
its validation, registers the type in the config allow-list and the
constructor map, and starts internal/provider/proxmox: the api seam and
its data types, providerIDs (vms/<vmid>/<name>) with the UID-derived VMID,
the description mark, state mapping, and error classification.

Tests read the responses captured from pv1-1 in Phase 0 rather than
repeating Proxmox's wording, and every matcher is run against every
captured error so none fires on the wrong message. The contract methods
are Transient stubs until Phases 5 to 7.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/provider/proxmox/mark.go

@@ -0,0 +1,54 @@
+package proxmox
+
+import (
+	"strings"
+	"time"
+
+	"gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/provider"
+)
+
+// createdAtKey is the third line of the mark; the first two use the
+// contract's label names.
+const createdAtKey = "proxy-operator-created-at"
+
+// instanceMark is the GC mark as read back from a VM's description (spec
+// entry 8).
+type instanceMark struct {
+	Managed   bool
+	UID       string
+	CreatedAt time.Time
+}
+
+// formatDescription renders the mark written in the clone call.
+func formatDescription(uid string, createdAt time.Time) string {
+	return provider.LabelManaged + "=" + provider.LabelManagedYes + "\n" +
+		provider.LabelUID + "=" + uid + "\n" +
+		createdAtKey + "=" + createdAt.UTC().Format(time.RFC3339)
+}
+
+// parseDescription reads key=value lines, tolerating CRLF, blank lines and
+// lines an admin added. The first occurrence of a key wins. Managed only
+// when the value is exactly LabelManagedYes; an unparsable created-at gives
+// the zero time, which GC treats as old.
+func parseDescription(desc string) instanceMark {
+	var m instanceMark
+	seen := map[string]bool{}
+	for line := range strings.SplitSeq(desc, "\n") {
+		key, value, ok := strings.Cut(strings.TrimSpace(line), "=")
+		if !ok || seen[key] {
+			continue
+		}
+		seen[key] = true
+		switch key {
+		case provider.LabelManaged:
+			m.Managed = value == provider.LabelManagedYes
+		case provider.LabelUID:
+			m.UID = value
+		case createdAtKey:
+			if t, err := time.Parse(time.RFC3339, value); err == nil {
+				m.CreatedAt = t
+			}
+		}
+	}
+	return m
+}