feat: Add @memoize decorator for caching method results

[guyca]

Summary

Add a new @memoize() decorator that caches method return values based on arguments, avoiding redundant computations for expensive operations.

• Supports both modern TC39 and legacy TypeScript decorator syntax
• Per-instance caching (each class instance maintains its own cache)
• Uses Object.is comparison (like React.useMemo) instead of JSON.stringify
• Single-value cache (caches only the last result)
• Optional custom isEqual function for specialized comparison logic

Usage

// Default: Object.is comparison for each argument
@memoize()
computeValue(a: number, b: number): number { ... }

// Custom equality function
@memoize({ isEqual: (newArgs, lastArgs) => newArgs[0].id === lastArgs[0].id })
getUserData(user: User): Data { ... }

Test plan

• Unit tests for caching behavior (same args return cached value)
• Tests for single-value cache behavior (eviction on different args)
• Tests for per-instance cache isolation
• Tests for various return types (objects, arrays, strings)
• Tests for Object.is edge cases (NaN, -0)
• Tests for custom isEqual function