feat(promise): add addJitter utility

[narukeu]

Adds addJitter(delay, factor = 0.2, rng = Math.random) to produce a symmetric randomized delay (uniform in [delay ± delay*factor], clamped ≥ 0) for retry/backoff/polling.

Changes

• New: addJitter.ts
• Export added in index.ts
• Tests: addJitter.spec.ts (range, non‑negative, deterministic RNG, zero factor, mean sanity)
• Docs: EN / zh_hans / ko / ja reference pages

[Copilot]

Pull Request Overview

Adds a new addJitter utility function to the promise module for introducing random jitter to delay values, helping prevent synchronized bursts in retry/backoff scenarios.

• Implements addJitter(delay, factor, rng) with uniform distribution and non-negative clamping
• Comprehensive test coverage including edge cases and statistical validation
• Full internationalization with documentation in English, Chinese, Korean, and Japanese

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/promise/index.ts	Exports the new addJitter function
src/promise/addJitter.ts	Core implementation with JSDoc documentation
src/promise/addJitter.spec.ts	Comprehensive test suite covering range validation, edge cases, and statistical properties
docs/reference/promise/addJitter.md	English documentation with examples
docs/zh_hans/reference/promise/addJitter.md	Chinese documentation
docs/ko/reference/promise/addJitter.md	Korean documentation
docs/ja/reference/promise/addJitter.md	Japanese documentation

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