Add once support to IStream

[ChrisWozniak]

Fixes #61

Summary

• Expose the existing EventEmitter once capability through the public IStream interface for report events.
• Add regression coverage that verifies the IStream type and one-time listener behavior.

Validation

• npx jest tests/unit/stream/stream/events.test.ts --runInBand (5 pass)
• npm run test:unit (19 suites, 390 tests passed)
• npx tsc --noEmit
• npm run lint
• npx prettier --check src/types/client.ts tests/unit/stream/stream/events.test.ts

Formatting baseline

The repository-wide npm run format:check reports CRLF formatting on 63 existing TypeScript files in this Windows checkout. The two changed files pass the scoped Prettier check; no unrelated formatting rewrite is included.

Scope

No runtime behavior, dependency, generator, example, or documentation changes.