Add Concurrent marker interface for tools

[CamilleScholtz]

Summary

Prism PHP supports concurrent tool execution via ->concurrent() on tools, allowing multiple I/O-bound tool calls to run in parallel using Laravel's Concurrency facade. However, the Laravel AI SDK has no way to expose this — createPrismTool() never calls ->concurrent().

This PR adds a Concurrent marker interface that tools can implement to opt-in to parallel execution.

Changes

• New Laravel\Ai\Contracts\Concurrent interface — empty marker interface following the existing pattern (HasTools, HasStructuredOutput, HasMiddleware, etc.)
• Modified AddsToolsToPrismRequests::createPrismTool() — checks if the tool implements Concurrent and calls ->concurrent() on the Prism tool
• Added tests — verifies concurrent tools get marked, and non-concurrent tools don't

Usage

use Laravel\Ai\Contracts\Concurrent;
use Laravel\Ai\Contracts\Tool;

class SearchPlacesTool implements Concurrent, Tool
{
    // Tool implementation...
}

When the AI model requests multiple tool calls in a single step, tools implementing Concurrent will execute in parallel rather than sequentially — reducing total wait time for I/O-bound operations like API calls, database queries, or file reads.

How it works

Prism groups tool calls by their concurrency flag. Concurrent tools are batched and executed via Concurrency::run() (Laravel's Concurrency facade), while sequential tools run one at a time. Results are returned in the original order regardless of execution timing. Error handling is identical for both — if one concurrent tool fails, others still complete.