Add machine inspection APIs and planner visualizer

[SandroMaglione]

Summary

• expose public getters for compiled state nodes, active snapshot configuration, and registered transition definitions without executing handlers
• allow object-form event, eventless, and completion handlers to declare an upper bound of target paths; inferred transition results are checked at compile time, while unknown declarations and unsafe runtime mismatches are rejected at runtime
• keep rendering outside core with an experimental text renderer that nests transitions beneath source states and distinguishes declared targets, no direct target, and dynamic handlers
• declare all 27 platformer transitions and cover its complete inspectable chart as an example of the API on a nested, parallel machine
• add a standalone planner visualizer that renders states and declared transitions, highlights the active configuration, and steps through enabled events with Machine.plan
• generate deterministic schema-valid event samples with Schema.toArbitrary, while allowing typed authored fixtures to override samples that need semantic values

Changeset

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

The visualizer-only commit does not need an additional changeset.

Validation

• pnpm check
• Relevant example checks, when examples changed
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed

Additional validation:

• pnpm check passed with 226 runtime tests, 105 type tests, strict consumer validation, and package verification
• pnpm perf:types passed; machine.handle measures 21,266 instantiations
• pnpm check passed in examples/platformer
• pnpm check passed in examples/visualizer with 8 tests, TypeScript validation, and a production Vite build
• the visualizer was exercised in a browser through initialization and a planned transition with no console warnings or errors