feat(safeJSONParse): add safe JSON parsing utility

[Yeom-JinHo]

Description

This PR introduces a new safeJSONParse utility that provides a non-throwing wrapper around JSON.parse, complementing the existing isJSON predicate.
The goal is to keep validation and transformation clearly separated while giving consumers a type-safe way to parse JSON strings.

Changes

• Added safeJSONParse<T = unknown>(value: unknown): T | null utility

  • Returns the parsed value when value is a string containing valid JSON
  • Returns null when value is not a string or when parsing fails
  • Mirrors JSON.parse semantics (e.g. "null" → null) while never throwing

• Implemented comprehensive runtime tests for safeJSONParse

  • Covers primitives, objects, arrays, nested structures, empty objects/arrays, and large numbers
  • Verifies failure cases for invalid JSON strings and non-string inputs
  • Ensures "null" input is handled as a valid JSON string whose parsed value is null

• Added type-level tests using expectTypeOf

  • Confirms that the generic parameter T is respected (T | null)
  • Verifies narrowing behavior after null checks
  • Asserts the default generic (T = unknown) when no type argument is provided

• Documented safeJSONParse in a dedicated MDX page

  • Usage examples with valid/invalid JSON strings and non-string inputs
  • Demonstrates generic usage with typed shapes (e.g. User)
  • Shows how to combine safeJSONParse with isJSON for clearer validation + parsing flows

Motivation

• Avoid duplicating try { JSON.parse(...) } catch { ... } patterns across the codebase
• Provide a clear separation of concerns:
  • isJSON(value) → “Is this a valid JSON string?” (pure validation)
  • safeJSONParse(value) → “Safely parse this JSON string into a value” (transformation)
• Improve ergonomics and type safety when dealing with unknown or loosely-typed inputs
• Align JSON-related utilities under a consistent API surface, where predicates live in the predicate category and non-throwing helpers live in the utility category