feat: Port Laravel's once() helper with coroutine safety

[binaryfire]

This PR ports Laravel's once() memoization helper to Hypervel, adapted for coroutine safety.

What's included

• Once class - Stores memoized values using Context instead of static properties, ensuring per-coroutine isolation
• Onceable class - Generates unique hashes from call traces to identify memoization targets
• once() helper - Same as Laravel's API: once(fn () => expensive())
• HasOnceHash contract - Allows objects to provide custom hash values for memoization

Coroutine safety

Laravel's implementation uses a static WeakMap which would leak state between concurrent requests in Swoole. This implementation stores the WeakMap in Context, so each coroutine gets its own isolated memoization cache.

// Each coroutine gets independent memoization
$result = once(fn () => $this->expensiveCalculation());

Tests

• OnceTest - Verifies caching behavior and coroutine isolation
• OnceableTest - Verifies trace-based hash generation and HasOnceHash support