Speed up VM create with work seeds

Beat VM create wall time without changing VM semantics.

Generate a work-seed ext4 sidecar during image builds and rootfs rebuilds, then clone and resize that seed for each new VM instead of rebuilding /root from scratch. Plumb the new seed artifact through config, runtime metadata, store state, runtime-bundle defaults, doctor checks, and default-image reconciliation so older images still fall back cleanly.

Add a daemon TAP pool to keep idle bridge-attached devices warm, expose stage timing in lifecycle logs, add a create/SSH benchmark script plus Make target, and teach verify.sh that tap-pool-* devices are reusable capacity rather than cleanup leaks.

Validated with go test ./..., make build, ./verify.sh, and make bench-create ARGS="--runs 2".

internal/model/types.go

@@ -42,12 +42,14 @@ type DaemonConfig struct {
 	NamegenPath         string
 	CustomizeScript     string
 	VSockPingHelperPath string
+	DefaultWorkSeed     string
 	AutoStopStaleAfter  time.Duration
 	StatsPollInterval   time.Duration
 	MetricsPollInterval time.Duration
 	BridgeName          string
 	BridgeIP            string
 	CIDR                string
+	TapPoolSize         int
 	DefaultDNS          string
 	DefaultImageName    string
 	DefaultRootfs       string
@@ -64,6 +66,7 @@ type Image struct {
 	Managed      bool      `json:"managed"`
 	ArtifactDir  string    `json:"artifact_dir,omitempty"`
 	RootfsPath   string    `json:"rootfs_path"`
+	WorkSeedPath string    `json:"work_seed_path,omitempty"`
 	KernelPath   string    `json:"kernel_path"`
 	InitrdPath   string    `json:"initrd_path,omitempty"`
 	ModulesDir   string    `json:"modules_dir,omitempty"`