[Cache][Routing] Add token bucket rate limiting with dynamic request cost

[Tresor-Kasenda]

This PR introduces native token bucket rate limiting to Laravel’s limiter stack, including HTTP middleware integration.

What’s new

• Added Limit::tokenBucket($capacity, $refillPerSecond) builder.
• Added TokenBucketLimit (capacity, refillPerSecond, cost(...)).
• Added token-bucket runtime APIs to Illuminate\Cache\RateLimiter:
  • tokenBucket(...)
  • remainingTokens(...)
  • availableInTokenBucket(...)
• Extended ThrottleRequests to support token bucket limits returned from named limiters.
• Added support for dynamic per-request token cost via closure.
• Updated ThrottleRequestsWithRedis to delegate to the parent middleware flow when token-bucket or after(...) callbacks are used.
• Updated Illuminate\Support\Facades\RateLimiter phpdoc accordingly.

Why

Current fixed-window / counter-based limits are sometimes too coarse for heterogeneous workloads.
Token bucket allows smoother traffic shaping and weighted request cost handling (e.g. expensive endpoints consume more tokens).

Example

RateLimiter::for('api', fn ($request) => Limit::tokenBucket(100, 10)
    ->by($request->user()?->id ?: $request->ip())
    ->cost(fn ($request) => $request->is('reports/*') ? 5 : 1));