Add suspend selector to get commands

[AkashKumar7902]

Closes #3886

What

• Add --suspend-selector=any|suspended|active to flux get, defaulting to any for backward-compatible output.
• Apply the selector consistently to named resources, leaf commands, aggregate commands, and watch events, in conjunction with label and status selectors.
• Read the native suspend field for Flux resources, the reconcile-disabled annotation for ArtifactGenerator, and classify ExternalArtifact as active because it has no suspension state.
• Add exhaustive adapter, command, aggregate, default-reset, invalid-input, and watch coverage.

This is a draft so maintainers can confirm the public flag name and the treatment of resource types without a native suspend field before it is marked ready.

Tests

• make tidy fmt vet && make test

Local testing

• Built baseline 1ed703a3 and signed candidate ef1fb5fd twice from commit-authenticated Git archives; each build pair was byte-identical and used SHA-bearing versions.
• Exercised both binaries against a real Kubernetes 1.36.2 envtest API.
• Verified baseline default output equals candidate default and explicit any output.
• Verified active/suspended leaf and aggregate partitions, label/status intersection, special resource semantics, invalid-value rejection before cluster access, and passive-only namespaces.
• Verified a real API watch suppresses enabled ArtifactGenerator events and emits disabled transitions.

Assisted-by: codex/gpt-5