Add TypeScript type performance checks

[SandroMaglione]

Summary

• add isolated Effect-only, import-only, defineStates, make, and handle type-performance fixtures
• add a dependency-free runner around tsc --extendedDiagnostics that reports total and marginal type instantiations
• add pnpm perf:types, which builds the package before measuring its public declarations
• add project guidance requiring before/after type-performance measurements for feature work

Why

Type safety and user-facing inference are core product concerns for effect-machine. These checks make the compiler cost of API changes visible without introducing another benchmarking dependency, while the agent guidance makes performance comparison part of the normal feature workflow.

Current results

Scenario                                  Instantiations  Marginal
Effect only                                           55  baseline
Import effect-machine                                 55        +0
Machine.defineStates (3 states)                    2,883    +2,828
Machine.make (3 states, 2 events)                  7,838    +4,947
machine.handle (3 states, 2 transitions)          17,314    +9,476

Check time remains informational because wall-clock measurements vary; instantiation counts are the stable comparison metric.

Validation

• pnpm perf:types
• pnpm typecheck
• pnpm test:types — 92 tests, 378 assertions
• Prettier check for all changed files