Add first-class choice pseudo-states

[SandroMaglione]

Summary

• add first-class, fully type-safe choice pseudo-states with typed target builders and ordinary TypeScript or Effect resolvers
• settle choices across initial, event, always, completion, history, chained, ancestor, and parallel transitions without exposing pseudo-states in stable snapshots
• extend inspection, traces, coverage, generated finite models, and the independent reference model with choice resolution evidence
• add comprehensive runtime and negative type tests, documentation, and a public-API changeset
• remove the standalone visualizer example

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Validation

• pnpm check
• Relevant example checks, when examples changed (the visualizer example was removed; no standalone package remains)
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed

Local pnpm perf:types passed on TypeScript 6.0.3, and the automated base-versus-PR report passed.