test(monitoring): fix failing snapshot tests and improve coverage

- Fix TestMonitor_PollGuestSnapshots_Coverage by correctly initializing State ID fields
- Improve PBS client to handle alternative datastore metric fields (total-space, etc.)
- Add comprehensive test coverage for PBS polling, auth failures, and datastore metrics
- Add various coverage tests for monitoring, alerts, and metadata handling
- Refactor Monitor to support better testing of client creation and auth handling

go.mod

@@ -38,12 +38,15 @@ require (
 require (
 	github.com/Microsoft/go-winio v0.4.21 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/buger/goterm v1.0.4 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/containerd/errdefs v1.0.0 // indirect
 	github.com/containerd/errdefs/pkg v0.3.0 // indirect
 	github.com/containerd/log v0.1.0 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/diskfs/go-diskfs v1.5.0 // indirect
 	github.com/distribution/reference v0.6.0 // indirect
+	github.com/djherbis/times v1.6.0 // indirect
 	github.com/docker/go-connections v0.6.0 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
@@ -65,11 +68,14 @@ require (
 	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.3 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/jinzhu/copier v0.3.4 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/klauspost/compress v1.18.2 // indirect
 	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
+	github.com/luthermonson/go-proxmox v0.3.1 // indirect
+	github.com/magefile/mage v1.14.0 // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect